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 $38.48   8.628%   $41.8001   $41.80   $41.80   $41.80  
  Purchase #2 $94.25   4.833%   $98.8051   $98.81   $98.80   $98.80  
  Purchase #3 $46.90   5.840%   $49.639   $49.64   $49.65   $49.60  
  Purchase #4 $213.42   11.859%   $238.7295   $238.73   $238.75   $238.70  
  Purchase #5 $13.41   10.527%   $14.8217   $14.82   $14.80   $14.80  
  Purchase #6 $171.70   4.561%   $179.5312   $179.53   $179.55   $179.50  
  Purchase #7 $113.46   8.601%   $123.2187   $123.22   $123.20   $123.20  
  7 purchase totals = $691.62       $746.5453   $746.55   $746.55   $746.40