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 $12.61   13.541%   $14.3175   $14.32   $14.30   $14.30  
  Purchase #2 $186.32   4.860%   $195.3752   $195.38   $195.40   $195.40  
  Purchase #3 $147.60   6.532%   $157.2412   $157.24   $157.25   $157.20  
  Purchase #4 $174.71   11.614%   $195.0008   $195.00   $195.00   $195.00  
  Purchase #5 $185.96   12.719%   $209.6123   $209.61   $209.60   $209.60  
  Purchase #6 $47.30   11.230%   $52.6118   $52.61   $52.60   $52.60  
  Purchase #7 $94.69   4.696%   $99.1366   $99.14   $99.15   $99.10  
  7 purchase totals = $849.19       $923.2954   $923.30   $923.30   $923.20