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 $58.97   12.857%   $66.5518   $66.55   $66.55   $66.60  
  Purchase #2 $163.62   10.339%   $180.5367   $180.54   $180.55   $180.50  
  Purchase #3 $134.94   10.517%   $149.1316   $149.13   $149.15   $149.10  
  Purchase #4 $177.56   11.346%   $197.706   $197.71   $197.70   $197.70  
  Purchase #5 $209.95   13.232%   $237.7306   $237.73   $237.75   $237.70  
  Purchase #6 $154.65   11.622%   $172.6234   $172.62   $172.60   $172.60  
  Purchase #7 $72.43   10.399%   $79.962   $79.96   $79.95   $80.00  
  7 purchase totals = $972.12       $1,084.2421   $1,084.24   $1,084.25   $1,084.20