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 $204.33   10.771%   $226.3384   $226.34   $226.35   $226.30  
  Purchase #2 $42.80   11.116%   $47.5576   $47.56   $47.55   $47.60  
  Purchase #3 $111.47   4.798%   $116.8183   $116.82   $116.80   $116.80  
  Purchase #4 $72.63   5.477%   $76.6079   $76.61   $76.60   $76.60  
  Purchase #5 $241.59   6.751%   $257.8997   $257.90   $257.90   $257.90  
  Purchase #6 $60.83   13.243%   $68.8857   $68.89   $68.90   $68.90  
  Purchase #7 $15.29   12.282%   $17.1679   $17.17   $17.15   $17.20  
  7 purchase totals = $748.94       $811.2755   $811.29   $811.25   $811.30