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 $118.91   11.204%   $132.2327   $132.23   $132.25   $132.20  
  Purchase #2 $168.88   13.533%   $191.7345   $191.73   $191.75   $191.70  
  Purchase #3 $239.60   13.429%   $271.7759   $271.78   $271.80   $271.80  
  Purchase #4 $106.76   13.502%   $121.1747   $121.17   $121.15   $121.20  
  Purchase #5 $45.71   6.225%   $48.5554   $48.56   $48.55   $48.60  
  Purchase #6 $103.73   3.614%   $107.4788   $107.48   $107.50   $107.50  
  Purchase #7 $126.42   11.756%   $141.2819   $141.28   $141.30   $141.30  
  7 purchase totals = $910.01       $1,014.2339   $1,014.23   $1,014.30   $1,014.30