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 $213.37   9.166%   $232.9275   $232.93   $232.95   $232.90  
  Purchase #2 $141.95   13.142%   $160.6051   $160.61   $160.60   $160.60  
  Purchase #3 $91.64   13.271%   $103.8015   $103.80   $103.80   $103.80  
  Purchase #4 $54.68   10.649%   $60.5029   $60.50   $60.50   $60.50  
  Purchase #5 $126.96   11.567%   $141.6455   $141.65   $141.65   $141.60  
  Purchase #6 $154.51   11.617%   $172.4594   $172.46   $172.45   $172.50  
  Purchase #7 $74.41   12.115%   $83.4248   $83.42   $83.40   $83.40  
  7 purchase totals = $857.52       $955.3667   $955.37   $955.35   $955.30