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 $103.46   10.598%   $114.4247   $114.42   $114.40   $114.40  
  Purchase #2 $151.92   3.579%   $157.3572   $157.36   $157.35   $157.40  
  Purchase #3 $41.30   12.340%   $46.3964   $46.40   $46.40   $46.40  
  Purchase #4 $91.97   3.714%   $95.3858   $95.39   $95.40   $95.40  
  Purchase #5 $221.72   7.288%   $237.879   $237.88   $237.90   $237.90  
  Purchase #6 $100.94   8.793%   $109.8157   $109.82   $109.80   $109.80  
  Purchase #7 $58.88   10.405%   $65.0065   $65.01   $65.00   $65.00  
  7 purchase totals = $770.19       $826.2653   $826.28   $826.25   $826.30