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 $86.61   11.615%   $96.6698   $96.67   $96.65   $96.70  
  Purchase #2 $120.91   12.474%   $135.9923   $135.99   $136.00   $136.00  
  Purchase #3 $238.29   5.812%   $252.1394   $252.14   $252.15   $252.10  
  Purchase #4 $43.34   6.469%   $46.1437   $46.14   $46.15   $46.10  
  Purchase #5 $113.78   10.102%   $125.2741   $125.27   $125.25   $125.30  
  Purchase #6 $228.64   7.398%   $245.5548   $245.55   $245.55   $245.60  
  Purchase #7 $43.96   3.512%   $45.5039   $45.50   $45.50   $45.50  
  7 purchase totals = $875.53       $947.2780   $947.26   $947.25   $947.30