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 $244.32   10.164%   $269.1527   $269.15   $269.15   $269.20  
  Purchase #2 $214.66   10.125%   $236.3943   $236.39   $236.40   $236.40  
  Purchase #3 $123.48   7.263%   $132.4484   $132.45   $132.45   $132.40  
  Purchase #4 $95.95   12.557%   $107.9984   $108.00   $108.00   $108.00  
  Purchase #5 $163.66   4.188%   $170.5141   $170.51   $170.50   $170.50  
  Purchase #6 $188.72   11.237%   $209.9265   $209.93   $209.95   $209.90  
  Purchase #7 $248.32   3.574%   $257.195   $257.20   $257.20   $257.20  
  7 purchase totals = $1,279.11       $1,383.6294   $1,383.63   $1,383.65   $1,383.60