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 $151.54   3.829%   $157.3425   $157.34   $157.35   $157.30  
  Purchase #2 $119.56   4.138%   $124.5074   $124.51   $124.50   $124.50  
  Purchase #3 $214.92   13.797%   $244.5725   $244.57   $244.55   $244.60  
  Purchase #4 $235.83   11.203%   $262.25   $262.25   $262.25   $262.30  
  Purchase #5 $184.65   5.757%   $195.2803   $195.28   $195.30   $195.30  
  Purchase #6 $161.70   6.633%   $172.4256   $172.43   $172.45   $172.40  
  Purchase #7 $112.35   12.289%   $126.1567   $126.16   $126.15   $126.20  
  7 purchase totals = $1,180.55       $1,282.5350   $1,282.54   $1,282.55   $1,282.60