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 $115.58   9.797%   $126.9034   $126.90   $126.90   $126.90  
  Purchase #2 $29.38   11.316%   $32.7046   $32.70   $32.70   $32.70  
  Purchase #3 $123.47   13.192%   $139.7582   $139.76   $139.75   $139.80  
  Purchase #4 $232.62   5.310%   $244.9721   $244.97   $244.95   $245.00  
  Purchase #5 $191.53   6.434%   $203.853   $203.85   $203.85   $203.90  
  Purchase #6 $84.39   11.150%   $93.7995   $93.80   $93.80   $93.80  
  Purchase #7 $59.42   12.712%   $66.9735   $66.97   $66.95   $67.00  
  7 purchase totals = $836.39       $908.9643   $908.95   $908.90   $909.10