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 $126.75   7.569%   $136.3437   $136.34   $136.35   $136.30  
  Purchase #2 $119.78   9.279%   $130.8944   $130.89   $130.90   $130.90  
  Purchase #3 $16.68   9.736%   $18.304   $18.30   $18.30   $18.30  
  Purchase #4 $229.39   7.439%   $246.4543   $246.45   $246.45   $246.50  
  Purchase #5 $92.30   11.501%   $102.9154   $102.92   $102.90   $102.90  
  Purchase #6 $58.84   8.761%   $63.995   $64.00   $64.00   $64.00  
  Purchase #7 $84.63   7.433%   $90.9205   $90.92   $90.90   $90.90  
  7 purchase totals = $728.37       $789.8273   $789.82   $789.80   $789.80