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 $69.53   8.785%   $75.6382   $75.64   $75.65   $75.60  
  Purchase #2 $245.25   3.652%   $254.2065   $254.21   $254.20   $254.20  
  Purchase #3 $185.38   6.599%   $197.6132   $197.61   $197.60   $197.60  
  Purchase #4 $241.32   7.786%   $260.1092   $260.11   $260.10   $260.10  
  Purchase #5 $83.87   12.605%   $94.4418   $94.44   $94.45   $94.40  
  Purchase #6 $157.73   13.447%   $178.94   $178.94   $178.95   $178.90  
  Purchase #7 $47.72   13.371%   $54.1006   $54.10   $54.10   $54.10  
  7 purchase totals = $1,030.80       $1,115.0495   $1,115.05   $1,115.05   $1,114.90