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 $92.64   6.207%   $98.3902   $98.39   $98.40   $98.40  
  Purchase #2 $245.48   7.169%   $263.0785   $263.08   $263.10   $263.10  
  Purchase #3 $151.62   4.559%   $158.5324   $158.53   $158.55   $158.50  
  Purchase #4 $183.41   3.539%   $189.9009   $189.90   $189.90   $189.90  
  Purchase #5 $126.32   10.278%   $139.3032   $139.30   $139.30   $139.30  
  Purchase #6 $250.78   6.546%   $267.1961   $267.20   $267.20   $267.20  
  Purchase #7 $109.68   9.603%   $120.2126   $120.21   $120.20   $120.20  
  7 purchase totals = $1,159.93       $1,236.6139   $1,236.61   $1,236.65   $1,236.60