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 $116.47   11.142%   $129.4471   $129.45   $129.45   $129.40  
  Purchase #2 $157.59   5.339%   $166.0037   $166.00   $166.00   $166.00  
  Purchase #3 $55.47   11.283%   $61.7287   $61.73   $61.75   $61.70  
  Purchase #4 $167.29   4.556%   $174.9117   $174.91   $174.90   $174.90  
  Purchase #5 $107.56   4.325%   $112.212   $112.21   $112.20   $112.20  
  Purchase #6 $248.79   7.680%   $267.8971   $267.90   $267.90   $267.90  
  Purchase #7 $35.97   8.450%   $39.0095   $39.01   $39.00   $39.00  
  7 purchase totals = $889.14       $951.2098   $951.21   $951.20   $951.10