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 $46.28   4.253%   $48.2483   $48.25   $48.25   $48.20  
  Purchase #2 $227.77   3.865%   $236.5733   $236.57   $236.55   $236.60  
  Purchase #3 $34.60   12.754%   $39.0129   $39.01   $39.00   $39.00  
  Purchase #4 $164.68   12.529%   $185.3128   $185.31   $185.30   $185.30  
  Purchase #5 $93.60   7.166%   $100.3074   $100.31   $100.30   $100.30  
  Purchase #6 $216.29   13.827%   $246.1964   $246.20   $246.20   $246.20  
  Purchase #7 $146.25   7.835%   $157.7087   $157.71   $157.70   $157.70  
  7 purchase totals = $929.47       $1,013.3598   $1,013.36   $1,013.30   $1,013.30