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 $173.93   9.560%   $190.5577   $190.56   $190.55   $190.60  
  Purchase #2 $203.94   5.495%   $215.1465   $215.15   $215.15   $215.10  
  Purchase #3 $76.34   6.702%   $81.4563   $81.46   $81.45   $81.50  
  Purchase #4 $172.70   9.135%   $188.4761   $188.48   $188.50   $188.50  
  Purchase #5 $179.63   5.624%   $189.7324   $189.73   $189.75   $189.70  
  Purchase #6 $118.69   7.770%   $127.9122   $127.91   $127.90   $127.90  
  Purchase #7 $237.73   4.314%   $247.9857   $247.99   $248.00   $248.00  
  7 purchase totals = $1,162.96       $1,241.2669   $1,241.28   $1,241.30   $1,241.30