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 $94.77   13.179%   $107.2597   $107.26   $107.25   $107.30  
  Purchase #2 $87.60   12.282%   $98.359   $98.36   $98.35   $98.40  
  Purchase #3 $223.51   11.497%   $249.2069   $249.21   $249.20   $249.20  
  Purchase #4 $29.82   7.483%   $32.0514   $32.05   $32.05   $32.10  
  Purchase #5 $62.96   6.359%   $66.9636   $66.96   $66.95   $67.00  
  Purchase #6 $178.37   6.763%   $190.4332   $190.43   $190.45   $190.40  
  Purchase #7 $47.89   11.394%   $53.3466   $53.35   $53.35   $53.30  
  7 purchase totals = $724.92       $797.6204   $797.62   $797.60   $797.70