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 $214.43   12.774%   $241.8213   $241.82   $241.80   $241.80  
  Purchase #2 $78.71   12.837%   $88.814   $88.81   $88.80   $88.80  
  Purchase #3 $162.55   12.681%   $183.163   $183.16   $183.15   $183.20  
  Purchase #4 $61.93   6.421%   $65.9065   $65.91   $65.90   $65.90  
  Purchase #5 $43.97   7.804%   $47.4014   $47.40   $47.40   $47.40  
  Purchase #6 $95.27   7.486%   $102.4019   $102.40   $102.40   $102.40  
  Purchase #7 $61.83   7.436%   $66.4277   $66.43   $66.45   $66.40  
  7 purchase totals = $718.69       $795.9358   $795.93   $795.90   $795.90