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 $204.73   10.804%   $226.849   $226.85   $226.85   $226.80  
  Purchase #2 $17.40   5.211%   $18.3067   $18.31   $18.30   $18.30  
  Purchase #3 $148.83   7.731%   $160.336   $160.34   $160.35   $160.30  
  Purchase #4 $174.53   7.620%   $187.8292   $187.83   $187.85   $187.80  
  Purchase #5 $75.38   8.479%   $81.7715   $81.77   $81.75   $81.80  
  Purchase #6 $74.76   10.151%   $82.3489   $82.35   $82.35   $82.30  
  Purchase #7 $127.80   10.375%   $141.0593   $141.06   $141.05   $141.10  
  7 purchase totals = $823.43       $898.5006   $898.51   $898.50   $898.40