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 $210.35   13.842%   $239.4666   $239.47   $239.45   $239.50  
  Purchase #2 $224.50   13.317%   $254.3967   $254.40   $254.40   $254.40  
  Purchase #3 $77.75   5.756%   $82.2253   $82.23   $82.25   $82.20  
  Purchase #4 $200.65   12.229%   $225.1875   $225.19   $225.20   $225.20  
  Purchase #5 $43.27   10.775%   $47.9323   $47.93   $47.95   $47.90  
  Purchase #6 $210.29   12.789%   $237.184   $237.18   $237.20   $237.20  
  Purchase #7 $98.97   13.532%   $112.3626   $112.36   $112.35   $112.40  
  7 purchase totals = $1,065.78       $1,198.7550   $1,198.76   $1,198.80   $1,198.80