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 $59.72   10.773%   $66.1536   $66.15   $66.15   $66.20  
  Purchase #2 $105.54   6.162%   $112.0434   $112.04   $112.05   $112.00  
  Purchase #3 $204.40   11.412%   $227.7261   $227.73   $227.75   $227.70  
  Purchase #4 $14.30   11.469%   $15.9401   $15.94   $15.95   $15.90  
  Purchase #5 $66.77   4.555%   $69.8114   $69.81   $69.80   $69.80  
  Purchase #6 $165.34   10.574%   $182.8231   $182.82   $182.80   $182.80  
  Purchase #7 $104.33   12.824%   $117.7093   $117.71   $117.70   $117.70  
  7 purchase totals = $720.40       $792.2070   $792.20   $792.20   $792.10