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 $239.88   9.118%   $261.7523   $261.75   $261.75   $261.80  
  Purchase #2 $226.33   4.351%   $236.1776   $236.18   $236.20   $236.20  
  Purchase #3 $35.97   8.515%   $39.0328   $39.03   $39.05   $39.00  
  Purchase #4 $97.35   6.332%   $103.5142   $103.51   $103.50   $103.50  
  Purchase #5 $205.46   8.184%   $222.2748   $222.27   $222.25   $222.30  
  Purchase #6 $91.77   7.711%   $98.8464   $98.85   $98.85   $98.80  
  Purchase #7 $164.31   12.112%   $184.2112   $184.21   $184.20   $184.20  
  7 purchase totals = $1,061.07       $1,145.8093   $1,145.80   $1,145.80   $1,145.80