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 $35.98   11.841%   $40.2404   $40.24   $40.25   $40.20  
  Purchase #2 $161.25   4.307%   $168.195   $168.20   $168.20   $168.20  
  Purchase #3 $91.63   12.303%   $102.9032   $102.90   $102.90   $102.90  
  Purchase #4 $198.30   4.277%   $206.7813   $206.78   $206.80   $206.80  
  Purchase #5 $110.71   4.309%   $115.4805   $115.48   $115.50   $115.50  
  Purchase #6 $37.31   12.264%   $41.8857   $41.89   $41.90   $41.90  
  Purchase #7 $214.54   11.623%   $239.476   $239.48   $239.50   $239.50  
  7 purchase totals = $849.72       $914.9621   $914.97   $915.05   $915.00