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 $89.87   13.627%   $102.1166   $102.12   $102.10   $102.10  
  Purchase #2 $64.43   6.622%   $68.6966   $68.70   $68.70   $68.70  
  Purchase #3 $60.36   13.120%   $68.2792   $68.28   $68.30   $68.30  
  Purchase #4 $91.85   6.705%   $98.0085   $98.01   $98.00   $98.00  
  Purchase #5 $183.60   11.801%   $205.2666   $205.27   $205.25   $205.30  
  Purchase #6 $84.26   9.751%   $92.4762   $92.48   $92.50   $92.50  
  Purchase #7 $207.44   9.251%   $226.6303   $226.63   $226.65   $226.60  
  7 purchase totals = $781.81       $861.4740   $861.49   $861.50   $861.50