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 $24.66   10.223%   $27.181   $27.18   $27.20   $27.20  
  Purchase #2 $41.43   5.189%   $43.5798   $43.58   $43.60   $43.60  
  Purchase #3 $165.63   4.799%   $173.5786   $173.58   $173.60   $173.60  
  Purchase #4 $193.79   8.113%   $209.5122   $209.51   $209.50   $209.50  
  Purchase #5 $193.51   6.502%   $206.092   $206.09   $206.10   $206.10  
  Purchase #6 $135.36   5.164%   $142.35   $142.35   $142.35   $142.40  
  Purchase #7 $191.64   8.827%   $208.5561   $208.56   $208.55   $208.60  
  7 purchase totals = $946.02       $1,010.8497   $1,010.85   $1,010.90   $1,011.00