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 $84.87   11.471%   $94.6054   $94.61   $94.60   $94.60  
  Purchase #2 $125.88   8.239%   $136.2513   $136.25   $136.25   $136.30  
  Purchase #3 $130.61   6.713%   $139.3778   $139.38   $139.40   $139.40  
  Purchase #4 $167.36   5.234%   $176.1196   $176.12   $176.10   $176.10  
  Purchase #5 $144.47   9.832%   $158.6743   $158.67   $158.65   $158.70  
  Purchase #6 $107.92   5.401%   $113.7488   $113.75   $113.75   $113.70  
  Purchase #7 $113.31   13.737%   $128.8754   $128.88   $128.90   $128.90  
  7 purchase totals = $874.42       $947.6526   $947.66   $947.65   $947.70