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 $168.80   13.356%   $191.3449   $191.34   $191.35   $191.30  
  Purchase #2 $161.38   10.328%   $178.0473   $178.05   $178.05   $178.00  
  Purchase #3 $120.30   5.494%   $126.9093   $126.91   $126.90   $126.90  
  Purchase #4 $228.36   9.183%   $249.3303   $249.33   $249.35   $249.30  
  Purchase #5 $141.53   3.266%   $146.1524   $146.15   $146.15   $146.20  
  Purchase #6 $106.88   12.711%   $120.4655   $120.47   $120.45   $120.50  
  Purchase #7 $213.38   4.853%   $223.7353   $223.74   $223.75   $223.70  
  7 purchase totals = $1,140.63       $1,235.9850   $1,235.99   $1,236.00   $1,235.90