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 $233.75   5.330%   $246.2089   $246.21   $246.20   $246.20  
  Purchase #2 $177.64   12.140%   $199.2055   $199.21   $199.20   $199.20  
  Purchase #3 $222.36   5.494%   $234.5765   $234.58   $234.60   $234.60  
  Purchase #4 $8.44   11.560%   $9.4157   $9.42   $9.40   $9.40  
  Purchase #5 $113.80   9.569%   $124.6895   $124.69   $124.70   $124.70  
  Purchase #6 $115.44   3.622%   $119.6212   $119.62   $119.60   $119.60  
  Purchase #7 $124.89   4.868%   $130.9696   $130.97   $130.95   $131.00  
  7 purchase totals = $996.32       $1,064.6869   $1,064.70   $1,064.65   $1,064.70