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 $225.58   13.762%   $256.6243   $256.62   $256.60   $256.60  
  Purchase #2 $58.78   12.546%   $66.1545   $66.15   $66.15   $66.20  
  Purchase #3 $121.96   10.486%   $134.7487   $134.75   $134.75   $134.70  
  Purchase #4 $26.37   13.718%   $29.9874   $29.99   $30.00   $30.00  
  Purchase #5 $102.72   11.720%   $114.7588   $114.76   $114.75   $114.80  
  Purchase #6 $133.44   11.169%   $148.3439   $148.34   $148.35   $148.30  
  Purchase #7 $158.76   11.589%   $177.1587   $177.16   $177.15   $177.20  
  7 purchase totals = $827.61       $927.7763   $927.77   $927.75   $927.80