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 $33.50   5.612%   $35.38   $35.38   $35.40   $35.40  
  Purchase #2 $248.54   9.360%   $271.8033   $271.80   $271.80   $271.80  
  Purchase #3 $37.39   7.316%   $40.1255   $40.13   $40.15   $40.10  
  Purchase #4 $62.72   11.358%   $69.8437   $69.84   $69.85   $69.80  
  Purchase #5 $145.73   5.130%   $153.2059   $153.21   $153.20   $153.20  
  Purchase #6 $51.89   12.735%   $58.4982   $58.50   $58.50   $58.50  
  Purchase #7 $121.62   11.710%   $135.8617   $135.86   $135.85   $135.90  
  7 purchase totals = $701.39       $764.7183   $764.72   $764.75   $764.70