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 $194.87   11.743%   $217.7536   $217.75   $217.75   $217.80  
  Purchase #2 $147.66   9.652%   $161.9121   $161.91   $161.90   $161.90  
  Purchase #3 $125.39   10.445%   $138.487   $138.49   $138.50   $138.50  
  Purchase #4 $92.60   6.164%   $98.3079   $98.31   $98.30   $98.30  
  Purchase #5 $84.70   6.645%   $90.3283   $90.33   $90.35   $90.30  
  Purchase #6 $46.91   5.316%   $49.4037   $49.40   $49.40   $49.40  
  Purchase #7 $174.86   7.588%   $188.1284   $188.13   $188.15   $188.10  
  7 purchase totals = $866.99       $944.3210   $944.32   $944.35   $944.30