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 $119.76   5.176%   $125.9588   $125.96   $125.95   $126.00  
  Purchase #2 $59.60   6.754%   $63.6254   $63.63   $63.65   $63.60  
  Purchase #3 $188.33   5.191%   $198.1062   $198.11   $198.10   $198.10  
  Purchase #4 $98.87   13.241%   $111.9614   $111.96   $111.95   $112.00  
  Purchase #5 $81.90   9.202%   $89.4364   $89.44   $89.45   $89.40  
  Purchase #6 $121.49   13.373%   $137.7369   $137.74   $137.75   $137.70  
  Purchase #7 $173.77   12.205%   $194.9786   $194.98   $195.00   $195.00  
  7 purchase totals = $843.72       $921.8037   $921.82   $921.85   $921.80