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 $24.66   13.743%   $28.049   $28.05   $28.05   $28.00  
  Purchase #2 $69.69   9.438%   $76.2673   $76.27   $76.25   $76.30  
  Purchase #3 $96.87   3.156%   $99.9272   $99.93   $99.95   $99.90  
  Purchase #4 $68.46   9.109%   $74.696   $74.70   $74.70   $74.70  
  Purchase #5 $62.66   9.198%   $68.4235   $68.42   $68.40   $68.40  
  Purchase #6 $93.91   4.310%   $97.9575   $97.96   $97.95   $98.00  
  Purchase #7 $234.87   11.662%   $262.2605   $262.26   $262.25   $262.30  
  7 purchase totals = $651.12       $707.5810   $707.59   $707.55   $707.60