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 $86.84   7.573%   $93.4164   $93.42   $93.40   $93.40  
  Purchase #2 $154.75   4.226%   $161.2897   $161.29   $161.30   $161.30  
  Purchase #3 $136.96   8.498%   $148.5989   $148.60   $148.60   $148.60  
  Purchase #4 $142.49   10.124%   $156.9157   $156.92   $156.90   $156.90  
  Purchase #5 $66.81   11.854%   $74.7297   $74.73   $74.75   $74.70  
  Purchase #6 $210.37   12.265%   $236.1719   $236.17   $236.15   $236.20  
  Purchase #7 $78.87   7.372%   $84.6843   $84.68   $84.70   $84.70  
  7 purchase totals = $877.09       $955.8066   $955.81   $955.80   $955.80