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 $187.37   11.616%   $209.1349   $209.13   $209.15   $209.10  
  Purchase #2 $64.61   5.157%   $67.9419   $67.94   $67.95   $67.90  
  Purchase #3 $63.44   7.873%   $68.4346   $68.43   $68.45   $68.40  
  Purchase #4 $98.73   9.439%   $108.0491   $108.05   $108.05   $108.00  
  Purchase #5 $189.72   10.844%   $210.2932   $210.29   $210.30   $210.30  
  Purchase #6 $11.69   11.377%   $13.02   $13.02   $13.00   $13.00  
  Purchase #7 $116.64   8.497%   $126.5509   $126.55   $126.55   $126.60  
  7 purchase totals = $732.20       $803.4246   $803.41   $803.45   $803.30