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 $183.32   12.358%   $205.9747   $205.97   $205.95   $206.00  
  Purchase #2 $51.68   13.474%   $58.6434   $58.64   $58.65   $58.60  
  Purchase #3 $128.30   5.461%   $135.3065   $135.31   $135.30   $135.30  
  Purchase #4 $94.43   3.246%   $97.4952   $97.50   $97.50   $97.50  
  Purchase #5 $170.60   9.368%   $186.5818   $186.58   $186.60   $186.60  
  Purchase #6 $62.90   4.755%   $65.8909   $65.89   $65.90   $65.90  
  Purchase #7 $182.25   6.581%   $194.2439   $194.24   $194.25   $194.20  
  7 purchase totals = $873.48       $944.1364   $944.13   $944.15   $944.10