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 $32.70   3.864%   $33.9635   $33.96   $33.95   $34.00  
  Purchase #2 $22.96   13.245%   $26.0011   $26.00   $26.00   $26.00  
  Purchase #3 $74.34   13.133%   $84.1031   $84.10   $84.10   $84.10  
  Purchase #4 $190.67   8.170%   $206.2477   $206.25   $206.25   $206.20  
  Purchase #5 $133.99   12.773%   $151.1045   $151.10   $151.10   $151.10  
  Purchase #6 $230.48   7.507%   $247.7821   $247.78   $247.80   $247.80  
  Purchase #7 $182.54   8.255%   $197.6087   $197.61   $197.60   $197.60  
  7 purchase totals = $867.68       $946.8107   $946.80   $946.80   $946.80