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 $237.70   10.733%   $263.2123   $263.21   $263.20   $263.20  
  Purchase #2 $124.79   6.134%   $132.4446   $132.44   $132.45   $132.40  
  Purchase #3 $97.46   8.737%   $105.9751   $105.98   $106.00   $106.00  
  Purchase #4 $60.92   11.634%   $68.0074   $68.01   $68.00   $68.00  
  Purchase #5 $35.45   12.695%   $39.9504   $39.95   $39.95   $40.00  
  Purchase #6 $177.38   5.316%   $186.8095   $186.81   $186.80   $186.80  
  Purchase #7 $131.56   7.788%   $141.8059   $141.81   $141.80   $141.80  
  7 purchase totals = $865.26       $938.2052   $938.21   $938.20   $938.20