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 $78.28   11.377%   $87.1859   $87.19   $87.20   $87.20  
  Purchase #2 $99.63   13.296%   $112.8768   $112.88   $112.90   $112.90  
  Purchase #3 $243.96   13.306%   $276.4213   $276.42   $276.40   $276.40  
  Purchase #4 $112.91   8.443%   $122.443   $122.44   $122.45   $122.40  
  Purchase #5 $210.40   8.635%   $228.568   $228.57   $228.55   $228.60  
  Purchase #6 $162.63   9.432%   $177.9693   $177.97   $177.95   $178.00  
  Purchase #7 $56.44   9.778%   $61.9587   $61.96   $61.95   $62.00  
  7 purchase totals = $964.25       $1,067.4230   $1,067.43   $1,067.40   $1,067.50