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 $59.45   13.160%   $67.2736   $67.27   $67.25   $67.30  
  Purchase #2 $22.37   3.549%   $23.1639   $23.16   $23.15   $23.20  
  Purchase #3 $215.41   4.622%   $225.3663   $225.37   $225.35   $225.40  
  Purchase #4 $92.79   11.501%   $103.4618   $103.46   $103.45   $103.50  
  Purchase #5 $138.98   11.488%   $154.946   $154.95   $154.95   $154.90  
  Purchase #6 $152.62   5.515%   $161.037   $161.04   $161.05   $161.00  
  Purchase #7 $246.89   4.169%   $257.1828   $257.18   $257.20   $257.20  
  7 purchase totals = $928.51       $992.4314   $992.43   $992.40   $992.50