Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $51.62   5.196%   $54.3022   $54.30   $54.30   $54.30  
  Purchase #2 $58.79   12.742%   $66.281   $66.28   $66.30   $66.30  
  Purchase #3 $211.44   12.447%   $237.7579   $237.76   $237.75   $237.80  
  Purchase #4 $97.85   13.121%   $110.6889   $110.69   $110.70   $110.70  
  Purchase #5 $198.49   6.307%   $211.0088   $211.01   $211.00   $211.00  
  Purchase #6 $189.98   11.390%   $211.6187   $211.62   $211.60   $211.60  
  Purchase #7 $168.75   11.570%   $188.2744   $188.27   $188.25   $188.30  
  7 purchase totals = $976.92       $1,079.9319   $1,079.93   $1,079.90   $1,080.00