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 $83.43   12.302%   $93.6936   $93.69   $93.70   $93.70  
  Purchase #2 $32.58   8.333%   $35.2949   $35.29   $35.30   $35.30  
  Purchase #3 $91.66   7.499%   $98.5336   $98.53   $98.55   $98.50  
  Purchase #4 $19.62   7.305%   $21.0532   $21.05   $21.05   $21.10  
  Purchase #5 $13.92   11.791%   $15.5613   $15.56   $15.55   $15.60  
  Purchase #6 $241.69   10.539%   $267.1617   $267.16   $267.15   $267.20  
  Purchase #7 $67.78   10.674%   $75.0148   $75.01   $75.00   $75.00  
  7 purchase totals = $550.68       $606.3131   $606.29   $606.30   $606.40