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 $116.63   8.765%   $126.8526   $126.85   $126.85   $126.90  
  Purchase #2 $24.97   11.378%   $27.8111   $27.81   $27.80   $27.80  
  Purchase #3 $112.83   5.778%   $119.3493   $119.35   $119.35   $119.30  
  Purchase #4 $236.42   13.306%   $267.878   $267.88   $267.90   $267.90  
  Purchase #5 $102.93   7.243%   $110.3852   $110.39   $110.40   $110.40  
  Purchase #6 $86.27   13.553%   $97.9622   $97.96   $97.95   $98.00  
  Purchase #7 $16.31   5.526%   $17.2113   $17.21   $17.20   $17.20  
  7 purchase totals = $696.36       $767.4497   $767.45   $767.45   $767.50