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 $233.25   3.323%   $241.0009   $241.00   $241.00   $241.00  
  Purchase #2 $188.95   9.853%   $207.5672   $207.57   $207.55   $207.60  
  Purchase #3 $63.68   12.586%   $71.6948   $71.69   $71.70   $71.70  
  Purchase #4 $60.31   8.813%   $65.6251   $65.63   $65.65   $65.60  
  Purchase #5 $241.63   6.272%   $256.785   $256.79   $256.80   $256.80  
  Purchase #6 $34.29   3.786%   $35.5882   $35.59   $35.60   $35.60  
  Purchase #7 $5.62   7.105%   $6.0193   $6.02   $6.00   $6.00  
  7 purchase totals = $827.73       $884.2805   $884.29   $884.30   $884.30