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 $116.69   8.843%   $127.0089   $127.01   $127.00   $127.00  
  Purchase #2 $139.71   12.211%   $156.77   $156.77   $156.75   $156.80  
  Purchase #3 $39.96   7.115%   $42.8032   $42.80   $42.80   $42.80  
  Purchase #4 $92.86   8.788%   $101.0205   $101.02   $101.00   $101.00  
  Purchase #5 $235.72   9.318%   $257.6844   $257.68   $257.70   $257.70  
  Purchase #6 $247.87   10.747%   $274.5086   $274.51   $274.50   $274.50  
  Purchase #7 $193.45   8.145%   $209.2065   $209.21   $209.20   $209.20  
  7 purchase totals = $1,066.26       $1,169.0021   $1,169.00   $1,168.95   $1,169.00