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 $204.78   7.308%   $219.7453   $219.75   $219.75   $219.70  
  Purchase #2 $214.69   11.619%   $239.6348   $239.63   $239.65   $239.60  
  Purchase #3 $121.35   6.675%   $129.4501   $129.45   $129.45   $129.50  
  Purchase #4 $200.42   7.621%   $215.694   $215.69   $215.70   $215.70  
  Purchase #5 $35.72   13.683%   $40.6076   $40.61   $40.60   $40.60  
  Purchase #6 $81.69   6.490%   $86.9917   $86.99   $87.00   $87.00  
  Purchase #7 $72.76   13.389%   $82.5018   $82.50   $82.50   $82.50  
  7 purchase totals = $931.41       $1,014.6253   $1,014.62   $1,014.65   $1,014.60