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 $114.89   12.515%   $129.2685   $129.27   $129.25   $129.30  
  Purchase #2 $69.26   5.667%   $73.185   $73.19   $73.20   $73.20  
  Purchase #3 $36.96   4.205%   $38.5142   $38.51   $38.50   $38.50  
  Purchase #4 $100.89   6.404%   $107.351   $107.35   $107.35   $107.40  
  Purchase #5 $209.62   9.478%   $229.4878   $229.49   $229.50   $229.50  
  Purchase #6 $184.64   12.110%   $206.9999   $207.00   $207.00   $207.00  
  Purchase #7 $137.82   10.177%   $151.8459   $151.85   $151.85   $151.80  
  7 purchase totals = $854.08       $936.6523   $936.66   $936.65   $936.70