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 $36.82   12.588%   $41.4549   $41.45   $41.45   $41.50  
  Purchase #2 $24.37   4.776%   $25.5339   $25.53   $25.55   $25.50  
  Purchase #3 $52.81   10.296%   $58.2473   $58.25   $58.25   $58.20  
  Purchase #4 $33.79   5.165%   $35.5353   $35.54   $35.55   $35.50  
  Purchase #5 $176.87   3.826%   $183.637   $183.64   $183.65   $183.60  
  Purchase #6 $148.63   4.237%   $154.9275   $154.93   $154.95   $154.90  
  Purchase #7 $241.99   11.578%   $270.0076   $270.01   $270.00   $270.00  
  7 purchase totals = $715.28       $769.3435   $769.35   $769.40   $769.20