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 $17.68   8.421%   $19.1688   $19.17   $19.15   $19.20  
  Purchase #2 $144.62   12.106%   $162.1277   $162.13   $162.15   $162.10  
  Purchase #3 $146.92   7.470%   $157.8949   $157.89   $157.90   $157.90  
  Purchase #4 $32.73   6.387%   $34.8205   $34.82   $34.80   $34.80  
  Purchase #5 $117.27   6.707%   $125.1353   $125.14   $125.15   $125.10  
  Purchase #6 $244.36   10.753%   $270.636   $270.64   $270.65   $270.60  
  Purchase #7 $60.97   4.129%   $63.4875   $63.49   $63.50   $63.50  
  7 purchase totals = $764.55       $833.2707   $833.28   $833.30   $833.20