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 $105.25   13.748%   $119.7198   $119.72   $119.70   $119.70  
  Purchase #2 $213.36   5.292%   $224.651   $224.65   $224.65   $224.70  
  Purchase #3 $58.90   4.393%   $61.4875   $61.49   $61.50   $61.50  
  Purchase #4 $108.28   10.677%   $119.8411   $119.84   $119.85   $119.80  
  Purchase #5 $54.95   4.462%   $57.4019   $57.40   $57.40   $57.40  
  Purchase #6 $145.47   8.360%   $157.6313   $157.63   $157.65   $157.60  
  Purchase #7 $224.51   7.344%   $240.998   $241.00   $241.00   $241.00  
  7 purchase totals = $910.72       $981.7306   $981.73   $981.75   $981.70