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 $67.26   13.315%   $76.2157   $76.22   $76.20   $76.20  
  Purchase #2 $178.73   5.836%   $189.1607   $189.16   $189.15   $189.20  
  Purchase #3 $173.68   12.804%   $195.918   $195.92   $195.90   $195.90  
  Purchase #4 $61.43   7.453%   $66.0084   $66.01   $66.00   $66.00  
  Purchase #5 $44.82   5.480%   $47.2761   $47.28   $47.30   $47.30  
  Purchase #6 $38.72   8.536%   $42.0251   $42.03   $42.05   $42.00  
  Purchase #7 $124.70   6.393%   $132.6721   $132.67   $132.65   $132.70  
  7 purchase totals = $689.34       $749.2761   $749.29   $749.25   $749.30