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 $84.95   9.862%   $93.3278   $93.33   $93.35   $93.30  
  Purchase #2 $103.42   8.486%   $112.1962   $112.20   $112.20   $112.20  
  Purchase #3 $203.83   5.660%   $215.3668   $215.37   $215.35   $215.40  
  Purchase #4 $25.64   3.509%   $26.5397   $26.54   $26.55   $26.50  
  Purchase #5 $124.32   13.277%   $140.826   $140.83   $140.85   $140.80  
  Purchase #6 $167.42   4.533%   $175.0091   $175.01   $175.00   $175.00  
  Purchase #7 $180.30   5.473%   $190.1678   $190.17   $190.15   $190.20  
  7 purchase totals = $889.88       $953.4334   $953.45   $953.45   $953.40