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 $81.48   13.856%   $92.7699   $92.77   $92.75   $92.80  
  Purchase #2 $93.44   12.203%   $104.8425   $104.84   $104.85   $104.80  
  Purchase #3 $136.95   6.418%   $145.7395   $145.74   $145.75   $145.70  
  Purchase #4 $153.85   4.291%   $160.4517   $160.45   $160.45   $160.50  
  Purchase #5 $10.82   13.200%   $12.2482   $12.25   $12.25   $12.20  
  Purchase #6 $64.48   11.164%   $71.6785   $71.68   $71.70   $71.70  
  Purchase #7 $136.69   12.758%   $154.1289   $154.13   $154.15   $154.10  
  7 purchase totals = $677.71       $741.8592   $741.86   $741.90   $741.80