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 $25.99   4.858%   $27.2526   $27.25   $27.25   $27.30  
  Purchase #2 $214.30   12.204%   $240.4532   $240.45   $240.45   $240.50  
  Purchase #3 $174.54   7.363%   $187.3914   $187.39   $187.40   $187.40  
  Purchase #4 $57.89   9.686%   $63.4972   $63.50   $63.50   $63.50  
  Purchase #5 $112.47   10.813%   $124.6314   $124.63   $124.65   $124.60  
  Purchase #6 $164.59   5.739%   $174.0358   $174.04   $174.05   $174.00  
  Purchase #7 $243.29   5.287%   $256.1527   $256.15   $256.15   $256.20  
  7 purchase totals = $993.07       $1,073.4143   $1,073.41   $1,073.45   $1,073.50