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 $152.91   4.455%   $159.7221   $159.72   $159.70   $159.70  
  Purchase #2 $194.97   13.598%   $221.482   $221.48   $221.50   $221.50  
  Purchase #3 $241.54   9.735%   $265.0539   $265.05   $265.05   $265.10  
  Purchase #4 $184.47   7.546%   $198.3901   $198.39   $198.40   $198.40  
  Purchase #5 $133.65   9.453%   $146.2839   $146.28   $146.30   $146.30  
  Purchase #6 $228.87   8.454%   $248.2187   $248.22   $248.20   $248.20  
  Purchase #7 $145.33   3.548%   $150.4863   $150.49   $150.50   $150.50  
  7 purchase totals = $1,281.74       $1,389.6370   $1,389.63   $1,389.65   $1,389.70