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 $83.97   12.690%   $94.6258   $94.63   $94.65   $94.60  
  Purchase #2 $150.31   4.457%   $157.0093   $157.01   $157.00   $157.00  
  Purchase #3 $47.83   3.846%   $49.6695   $49.67   $49.65   $49.70  
  Purchase #4 $225.72   10.423%   $249.2468   $249.25   $249.25   $249.20  
  Purchase #5 $60.83   7.870%   $65.6173   $65.62   $65.60   $65.60  
  Purchase #6 $178.51   3.788%   $185.272   $185.27   $185.25   $185.30  
  Purchase #7 $28.76   12.203%   $32.2696   $32.27   $32.25   $32.30  
  7 purchase totals = $775.93       $833.7103   $833.72   $833.65   $833.70