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 $127.84   4.591%   $133.7091   $133.71   $133.70   $133.70  
  Purchase #2 $101.38   6.802%   $108.2759   $108.28   $108.30   $108.30  
  Purchase #3 $146.45   7.721%   $157.7574   $157.76   $157.75   $157.80  
  Purchase #4 $170.69   5.742%   $180.491   $180.49   $180.50   $180.50  
  Purchase #5 $60.99   5.424%   $64.2981   $64.30   $64.30   $64.30  
  Purchase #6 $250.87   5.192%   $263.8952   $263.90   $263.90   $263.90  
  Purchase #7 $97.63   9.697%   $107.0972   $107.10   $107.10   $107.10  
  7 purchase totals = $955.85       $1,015.5239   $1,015.54   $1,015.55   $1,015.60