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 $135.53   7.806%   $146.1095   $146.11   $146.10   $146.10  
  Purchase #2 $19.34   11.724%   $21.6074   $21.61   $21.60   $21.60  
  Purchase #3 $98.48   4.150%   $102.5669   $102.57   $102.55   $102.60  
  Purchase #4 $213.63   4.351%   $222.925   $222.93   $222.95   $222.90  
  Purchase #5 $22.64   3.177%   $23.3593   $23.36   $23.35   $23.40  
  Purchase #6 $246.62   12.253%   $276.8383   $276.84   $276.85   $276.80  
  Purchase #7 $222.87   7.627%   $239.8683   $239.87   $239.85   $239.90  
  7 purchase totals = $959.11       $1,033.2747   $1,033.29   $1,033.25   $1,033.30