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 $86.65   8.829%   $94.3003   $94.30   $94.30   $94.30  
  Purchase #2 $192.25   5.134%   $202.1201   $202.12   $202.10   $202.10  
  Purchase #3 $90.30   7.845%   $97.384   $97.38   $97.40   $97.40  
  Purchase #4 $141.40   4.830%   $148.2296   $148.23   $148.25   $148.20  
  Purchase #5 $53.67   7.144%   $57.5042   $57.50   $57.50   $57.50  
  Purchase #6 $200.80   4.351%   $209.5368   $209.54   $209.55   $209.50  
  Purchase #7 $74.73   4.596%   $78.1646   $78.16   $78.15   $78.20  
  7 purchase totals = $839.80       $887.2396   $887.23   $887.25   $887.20