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 $241.57   12.154%   $270.9304   $270.93   $270.95   $270.90  
  Purchase #2 $192.48   11.364%   $214.3534   $214.35   $214.35   $214.40  
  Purchase #3 $29.44   12.269%   $33.052   $33.05   $33.05   $33.10  
  Purchase #4 $241.74   11.116%   $268.6118   $268.61   $268.60   $268.60  
  Purchase #5 $96.80   4.367%   $101.0273   $101.03   $101.05   $101.00  
  Purchase #6 $150.56   4.387%   $157.1651   $157.17   $157.15   $157.20  
  Purchase #7 $211.66   11.868%   $236.7798   $236.78   $236.80   $236.80  
  7 purchase totals = $1,164.25       $1,281.9198   $1,281.92   $1,281.95   $1,282.00