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 $63.87   3.259%   $65.9515   $65.95   $65.95   $66.00  
  Purchase #2 $174.53   9.855%   $191.7299   $191.73   $191.75   $191.70  
  Purchase #3 $90.38   12.119%   $101.3332   $101.33   $101.35   $101.30  
  Purchase #4 $89.26   8.694%   $97.0203   $97.02   $97.00   $97.00  
  Purchase #5 $249.78   13.676%   $283.9399   $283.94   $283.95   $283.90  
  Purchase #6 $126.66   10.501%   $139.9606   $139.96   $139.95   $140.00  
  Purchase #7 $247.77   10.614%   $274.0683   $274.07   $274.05   $274.10  
  7 purchase totals = $1,042.25       $1,154.0037   $1,154.00   $1,154.00   $1,154.00