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 $61.88   7.462%   $66.4975   $66.50   $66.50   $66.50  
  Purchase #2 $170.71   5.770%   $180.56   $180.56   $180.55   $180.60  
  Purchase #3 $60.34   9.172%   $65.8744   $65.87   $65.85   $65.90  
  Purchase #4 $115.76   12.272%   $129.9661   $129.97   $129.95   $130.00  
  Purchase #5 $98.45   11.679%   $109.948   $109.95   $109.95   $109.90  
  Purchase #6 $41.70   9.557%   $45.6853   $45.69   $45.70   $45.70  
  Purchase #7 $131.97   4.315%   $137.6645   $137.66   $137.65   $137.70  
  7 purchase totals = $680.81       $736.1958   $736.20   $736.15   $736.30