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 $63.96   7.143%   $68.5287   $68.53   $68.55   $68.50  
  Purchase #2 $149.90   13.283%   $169.8112   $169.81   $169.80   $169.80  
  Purchase #3 $43.56   5.819%   $46.0948   $46.09   $46.10   $46.10  
  Purchase #4 $222.94   5.576%   $235.3711   $235.37   $235.35   $235.40  
  Purchase #5 $76.41   7.243%   $81.9444   $81.94   $81.95   $81.90  
  Purchase #6 $133.58   11.526%   $148.9764   $148.98   $149.00   $149.00  
  Purchase #7 $47.93   11.326%   $53.3586   $53.36   $53.35   $53.40  
  7 purchase totals = $738.28       $804.0852   $804.08   $804.10   $804.10