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 $14.84   13.559%   $16.8522   $16.85   $16.85   $16.90  
  Purchase #2 $140.65   4.184%   $146.5348   $146.53   $146.55   $146.50  
  Purchase #3 $84.28   9.669%   $92.429   $92.43   $92.45   $92.40  
  Purchase #4 $197.45   5.215%   $207.747   $207.75   $207.75   $207.70  
  Purchase #5 $102.40   12.534%   $115.2348   $115.23   $115.25   $115.20  
  Purchase #6 $59.94   8.399%   $64.9744   $64.97   $64.95   $65.00  
  Purchase #7 $229.28   5.788%   $242.5507   $242.55   $242.55   $242.60  
  7 purchase totals = $828.84       $886.3229   $886.31   $886.35   $886.30