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 $124.63   12.419%   $140.1078   $140.11   $140.10   $140.10  
  Purchase #2 $115.43   13.358%   $130.8491   $130.85   $130.85   $130.80  
  Purchase #3 $110.89   7.463%   $119.1657   $119.17   $119.15   $119.20  
  Purchase #4 $159.29   11.340%   $177.3535   $177.35   $177.35   $177.40  
  Purchase #5 $114.69   8.312%   $124.223   $124.22   $124.20   $124.20  
  Purchase #6 $128.83   6.250%   $136.8819   $136.88   $136.90   $136.90  
  Purchase #7 $222.87   11.233%   $247.905   $247.91   $247.90   $247.90  
  7 purchase totals = $976.63       $1,076.4860   $1,076.49   $1,076.45   $1,076.50