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 $242.30   10.444%   $267.6058   $267.61   $267.60   $267.60  
  Purchase #2 $229.47   8.465%   $248.8946   $248.89   $248.90   $248.90  
  Purchase #3 $174.64   5.422%   $184.109   $184.11   $184.10   $184.10  
  Purchase #4 $61.97   7.361%   $66.5316   $66.53   $66.55   $66.50  
  Purchase #5 $136.30   7.682%   $146.7706   $146.77   $146.75   $146.80  
  Purchase #6 $230.37   7.277%   $247.134   $247.13   $247.15   $247.10  
  Purchase #7 $239.60   8.407%   $259.7432   $259.74   $259.75   $259.70  
  7 purchase totals = $1,314.65       $1,420.7888   $1,420.78   $1,420.80   $1,420.70