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 $130.31   8.611%   $141.531   $141.53   $141.55   $141.50  
  Purchase #2 $144.37   9.268%   $157.7502   $157.75   $157.75   $157.80  
  Purchase #3 $85.31   13.384%   $96.7279   $96.73   $96.75   $96.70  
  Purchase #4 $21.48   11.280%   $23.9029   $23.90   $23.90   $23.90  
  Purchase #5 $72.93   9.856%   $80.118   $80.12   $80.10   $80.10  
  Purchase #6 $74.44   7.686%   $80.1615   $80.16   $80.15   $80.20  
  Purchase #7 $32.97   13.619%   $37.4602   $37.46   $37.45   $37.50  
  7 purchase totals = $561.81       $617.6517   $617.65   $617.65   $617.70