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 $241.88   9.621%   $265.1513   $265.15   $265.15   $265.20  
  Purchase #2 $18.51   10.647%   $20.4808   $20.48   $20.50   $20.50  
  Purchase #3 $87.36   6.216%   $92.7903   $92.79   $92.80   $92.80  
  Purchase #4 $142.25   10.853%   $157.6884   $157.69   $157.70   $157.70  
  Purchase #5 $13.61   9.434%   $14.894   $14.89   $14.90   $14.90  
  Purchase #6 $175.75   9.556%   $192.5447   $192.54   $192.55   $192.50  
  Purchase #7 $185.66   8.430%   $201.3111   $201.31   $201.30   $201.30  
  7 purchase totals = $865.02       $944.8606   $944.85   $944.90   $944.90