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 $194.95   13.741%   $221.7381   $221.74   $221.75   $221.70  
  Purchase #2 $53.66   3.195%   $55.3744   $55.37   $55.35   $55.40  
  Purchase #3 $139.77   11.665%   $156.0742   $156.07   $156.05   $156.10  
  Purchase #4 $116.83   11.219%   $129.9372   $129.94   $129.95   $129.90  
  Purchase #5 $43.50   8.584%   $47.234   $47.23   $47.25   $47.20  
  Purchase #6 $156.68   6.438%   $166.7671   $166.77   $166.75   $166.80  
  Purchase #7 $19.45   5.628%   $20.5446   $20.54   $20.55   $20.50  
  7 purchase totals = $724.84       $797.6696   $797.66   $797.65   $797.60