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   8.521%   $262.4906   $262.49   $262.50   $262.50  
  Purchase #2 $246.36   13.256%   $279.0175   $279.02   $279.00   $279.00  
  Purchase #3 $216.57   4.207%   $225.6811   $225.68   $225.70   $225.70  
  Purchase #4 $115.26   8.288%   $124.8127   $124.81   $124.80   $124.80  
  Purchase #5 $151.80   10.813%   $168.2141   $168.21   $168.20   $168.20  
  Purchase #6 $183.69   5.804%   $194.3514   $194.35   $194.35   $194.40  
  Purchase #7 $149.41   3.827%   $155.1279   $155.13   $155.15   $155.10  
  7 purchase totals = $1,304.97       $1,409.6953   $1,409.69   $1,409.70   $1,409.70