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 $84.29   10.660%   $93.2753   $93.28   $93.30   $93.30  
  Purchase #2 $152.71   13.723%   $173.6664   $173.67   $173.65   $173.70  
  Purchase #3 $210.40   6.526%   $224.1307   $224.13   $224.15   $224.10  
  Purchase #4 $13.86   11.529%   $15.4579   $15.46   $15.45   $15.50  
  Purchase #5 $85.28   13.127%   $96.4747   $96.47   $96.45   $96.50  
  Purchase #6 $5.28   3.423%   $5.4607   $5.46   $5.45   $5.50  
  Purchase #7 $218.99   9.845%   $240.5496   $240.55   $240.55   $240.50  
  7 purchase totals = $770.81       $849.0153   $849.02   $849.00   $849.10