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 $207.97   13.726%   $236.516   $236.52   $236.50   $236.50  
  Purchase #2 $162.97   8.291%   $176.4818   $176.48   $176.50   $176.50  
  Purchase #3 $162.95   12.691%   $183.63   $183.63   $183.65   $183.60  
  Purchase #4 $81.54   10.420%   $90.0365   $90.04   $90.05   $90.00  
  Purchase #5 $216.42   5.120%   $227.5007   $227.50   $227.50   $227.50  
  Purchase #6 $214.27   8.293%   $232.0394   $232.04   $232.05   $232.00  
  Purchase #7 $25.37   8.361%   $27.4912   $27.49   $27.50   $27.50  
  7 purchase totals = $1,071.49       $1,173.6956   $1,173.70   $1,173.75   $1,173.60