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 $23.96   8.524%   $26.0024   $26.00   $26.00   $26.00  
  Purchase #2 $144.90   13.396%   $164.3108   $164.31   $164.30   $164.30  
  Purchase #3 $203.97   4.716%   $213.5892   $213.59   $213.60   $213.60  
  Purchase #4 $128.53   5.316%   $135.3627   $135.36   $135.35   $135.40  
  Purchase #5 $96.56   4.533%   $100.9371   $100.94   $100.95   $100.90  
  Purchase #6 $82.81   10.308%   $91.3461   $91.35   $91.35   $91.30  
  Purchase #7 $71.59   11.131%   $79.5587   $79.56   $79.55   $79.60  
  7 purchase totals = $752.32       $811.1070   $811.11   $811.10   $811.10