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 $243.60   13.535%   $276.5713   $276.57   $276.55   $276.60  
  Purchase #2 $216.34   4.322%   $225.6902   $225.69   $225.70   $225.70  
  Purchase #3 $233.97   4.555%   $244.6273   $244.63   $244.65   $244.60  
  Purchase #4 $197.40   5.770%   $208.79   $208.79   $208.80   $208.80  
  Purchase #5 $85.25   11.579%   $95.1211   $95.12   $95.10   $95.10  
  Purchase #6 $201.78   11.398%   $224.7789   $224.78   $224.80   $224.80  
  Purchase #7 $214.50   7.705%   $231.0272   $231.03   $231.05   $231.00  
  7 purchase totals = $1,392.84       $1,506.6060   $1,506.61   $1,506.65   $1,506.60