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 $210.95   11.391%   $234.9793   $234.98   $235.00   $235.00  
  Purchase #2 $8.76   13.333%   $9.928   $9.93   $9.95   $9.90  
  Purchase #3 $51.46   3.671%   $53.3491   $53.35   $53.35   $53.30  
  Purchase #4 $103.46   6.414%   $110.0959   $110.10   $110.10   $110.10  
  Purchase #5 $164.89   5.739%   $174.353   $174.35   $174.35   $174.40  
  Purchase #6 $107.40   8.242%   $116.2519   $116.25   $116.25   $116.30  
  Purchase #7 $79.44   6.571%   $84.66   $84.66   $84.65   $84.70  
  7 purchase totals = $726.36       $783.6172   $783.62   $783.65   $783.70