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 $64.91   6.839%   $69.3492   $69.35   $69.35   $69.30  
  Purchase #2 $103.65   13.166%   $117.2966   $117.30   $117.30   $117.30  
  Purchase #3 $113.38   6.321%   $120.5467   $120.55   $120.55   $120.50  
  Purchase #4 $67.84   12.296%   $76.1816   $76.18   $76.20   $76.20  
  Purchase #5 $49.53   9.427%   $54.1992   $54.20   $54.20   $54.20  
  Purchase #6 $58.73   10.486%   $64.8884   $64.89   $64.90   $64.90  
  Purchase #7 $202.78   3.275%   $209.421   $209.42   $209.40   $209.40  
  7 purchase totals = $660.82       $711.8827   $711.89   $711.90   $711.80