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 $125.91   11.172%   $139.9767   $139.98   $140.00   $140.00  
  Purchase #2 $206.87   5.186%   $217.5983   $217.60   $217.60   $217.60  
  Purchase #3 $127.95   5.295%   $134.725   $134.73   $134.75   $134.70  
  Purchase #4 $249.76   12.646%   $281.3446   $281.34   $281.35   $281.30  
  Purchase #5 $172.60   7.348%   $185.2826   $185.28   $185.30   $185.30  
  Purchase #6 $194.81   13.813%   $221.7191   $221.72   $221.70   $221.70  
  Purchase #7 $96.94   7.661%   $104.3666   $104.37   $104.35   $104.40  
  7 purchase totals = $1,174.84       $1,285.0129   $1,285.02   $1,285.05   $1,285.00