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 $202.57   6.130%   $214.9875   $214.99   $215.00   $215.00  
  Purchase #2 $97.47   3.378%   $100.7625   $100.76   $100.75   $100.80  
  Purchase #3 $112.53   7.650%   $121.1385   $121.14   $121.15   $121.10  
  Purchase #4 $124.80   6.256%   $132.6075   $132.61   $132.60   $132.60  
  Purchase #5 $160.76   6.832%   $171.7431   $171.74   $171.75   $171.70  
  Purchase #6 $67.87   8.428%   $73.5901   $73.59   $73.60   $73.60  
  Purchase #7 $101.39   5.541%   $107.008   $107.01   $107.00   $107.00  
  7 purchase totals = $867.39       $921.8372   $921.84   $921.85   $921.80