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 $54.26   11.657%   $60.5851   $60.59   $60.60   $60.60  
  Purchase #2 $246.35   10.867%   $273.1209   $273.12   $273.10   $273.10  
  Purchase #3 $100.97   11.569%   $112.6512   $112.65   $112.65   $112.70  
  Purchase #4 $174.76   11.612%   $195.0531   $195.05   $195.05   $195.10  
  Purchase #5 $30.69   10.609%   $33.9459   $33.95   $33.95   $33.90  
  Purchase #6 $214.51   12.554%   $241.4396   $241.44   $241.45   $241.40  
  Purchase #7 $236.42   6.802%   $252.5013   $252.50   $252.50   $252.50  
  7 purchase totals = $1,057.96       $1,169.2971   $1,169.30   $1,169.30   $1,169.30