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 $238.83   6.559%   $254.4949   $254.49   $254.50   $254.50  
  Purchase #2 $57.82   7.552%   $62.1866   $62.19   $62.20   $62.20  
  Purchase #3 $154.73   3.692%   $160.4426   $160.44   $160.45   $160.40  
  Purchase #4 $128.36   3.813%   $133.2544   $133.25   $133.25   $133.30  
  Purchase #5 $92.37   9.671%   $101.3031   $101.30   $101.30   $101.30  
  Purchase #6 $144.68   5.230%   $152.2468   $152.25   $152.25   $152.20  
  Purchase #7 $162.34   6.487%   $172.871   $172.87   $172.85   $172.90  
  7 purchase totals = $979.13       $1,036.7994   $1,036.79   $1,036.80   $1,036.80