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 $207.82   3.244%   $214.5617   $214.56   $214.55   $214.60  
  Purchase #2 $34.72   12.614%   $39.0996   $39.10   $39.10   $39.10  
  Purchase #3 $61.36   5.179%   $64.5378   $64.54   $64.55   $64.50  
  Purchase #4 $249.68   8.703%   $271.4097   $271.41   $271.40   $271.40  
  Purchase #5 $248.36   7.664%   $267.3943   $267.39   $267.40   $267.40  
  Purchase #6 $15.34   3.601%   $15.8924   $15.89   $15.90   $15.90  
  Purchase #7 $150.91   7.251%   $161.8525   $161.85   $161.85   $161.90  
  7 purchase totals = $968.19       $1,034.7480   $1,034.74   $1,034.75   $1,034.80