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 $60.92   8.346%   $66.0044   $66.00   $66.00   $66.00  
  Purchase #2 $125.81   3.859%   $130.665   $130.67   $130.65   $130.70  
  Purchase #3 $213.36   4.387%   $222.7201   $222.72   $222.70   $222.70  
  Purchase #4 $216.28   9.282%   $236.3551   $236.36   $236.35   $236.40  
  Purchase #5 $29.57   3.153%   $30.5023   $30.50   $30.50   $30.50  
  Purchase #6 $105.88   12.823%   $119.457   $119.46   $119.45   $119.50  
  Purchase #7 $250.85   7.150%   $268.7858   $268.79   $268.80   $268.80  
  7 purchase totals = $1,002.67       $1,074.4897   $1,074.50   $1,074.45   $1,074.60