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 $31.82   11.123%   $35.3593   $35.36   $35.35   $35.40  
  Purchase #2 $69.53   9.639%   $76.232   $76.23   $76.25   $76.20  
  Purchase #3 $88.38   4.815%   $92.6355   $92.64   $92.65   $92.60  
  Purchase #4 $14.96   13.262%   $16.944   $16.94   $16.95   $16.90  
  Purchase #5 $62.38   12.149%   $69.9585   $69.96   $69.95   $70.00  
  Purchase #6 $195.54   3.383%   $202.1551   $202.16   $202.15   $202.20  
  Purchase #7 $231.89   12.127%   $260.0113   $260.01   $260.00   $260.00  
  7 purchase totals = $694.50       $753.2957   $753.30   $753.30   $753.30