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 $24.67   5.285%   $25.9738   $25.97   $25.95   $26.00  
  Purchase #2 $49.77   11.244%   $55.3661   $55.37   $55.35   $55.40  
  Purchase #3 $239.92   8.536%   $260.3996   $260.40   $260.40   $260.40  
  Purchase #4 $157.69   11.573%   $175.9395   $175.94   $175.95   $175.90  
  Purchase #5 $40.73   13.791%   $46.3471   $46.35   $46.35   $46.30  
  Purchase #6 $203.28   3.148%   $209.6793   $209.68   $209.70   $209.70  
  Purchase #7 $135.76   10.737%   $150.3366   $150.34   $150.35   $150.30  
  7 purchase totals = $851.82       $924.0420   $924.05   $924.05   $924.00