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 $110.62   5.327%   $116.5127   $116.51   $116.50   $116.50  
  Purchase #2 $61.83   4.375%   $64.5351   $64.54   $64.55   $64.50  
  Purchase #3 $70.46   6.399%   $74.9687   $74.97   $74.95   $75.00  
  Purchase #4 $54.78   4.725%   $57.3684   $57.37   $57.35   $57.40  
  Purchase #5 $215.29   9.722%   $236.2205   $236.22   $236.20   $236.20  
  Purchase #6 $38.26   12.425%   $43.0138   $43.01   $43.00   $43.00  
  Purchase #7 $210.28   5.712%   $222.2912   $222.29   $222.30   $222.30  
  7 purchase totals = $761.52       $814.9104   $814.91   $814.85   $814.90