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 $54.25   13.586%   $61.6204   $61.62   $61.60   $61.60  
  Purchase #2 $242.98   13.344%   $275.4033   $275.40   $275.40   $275.40  
  Purchase #3 $115.69   11.671%   $129.1922   $129.19   $129.20   $129.20  
  Purchase #4 $188.42   6.716%   $201.0743   $201.07   $201.05   $201.10  
  Purchase #5 $164.59   9.487%   $180.2047   $180.20   $180.20   $180.20  
  Purchase #6 $65.30   7.862%   $70.4339   $70.43   $70.45   $70.40  
  Purchase #7 $14.41   10.123%   $15.8687   $15.87   $15.85   $15.90  
  7 purchase totals = $845.64       $933.7975   $933.78   $933.75   $933.80