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 $221.73   11.670%   $247.6059   $247.61   $247.60   $247.60  
  Purchase #2 $74.28   12.382%   $83.4773   $83.48   $83.50   $83.50  
  Purchase #3 $173.88   12.359%   $195.3698   $195.37   $195.35   $195.40  
  Purchase #4 $181.37   3.826%   $188.3092   $188.31   $188.30   $188.30  
  Purchase #5 $193.77   4.194%   $201.8967   $201.90   $201.90   $201.90  
  Purchase #6 $163.35   13.790%   $185.876   $185.88   $185.90   $185.90  
  Purchase #7 $215.47   5.380%   $227.0623   $227.06   $227.05   $227.10  
  7 purchase totals = $1,223.85       $1,329.5972   $1,329.61   $1,329.60   $1,329.70