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 $244.28   9.198%   $266.7489   $266.75   $266.75   $266.70  
  Purchase #2 $135.65   12.691%   $152.8653   $152.87   $152.85   $152.90  
  Purchase #3 $8.41   8.377%   $9.1145   $9.11   $9.10   $9.10  
  Purchase #4 $238.62   3.151%   $246.1389   $246.14   $246.15   $246.10  
  Purchase #5 $168.34   5.105%   $176.9338   $176.93   $176.95   $176.90  
  Purchase #6 $190.77   12.177%   $214.0001   $214.00   $214.00   $214.00  
  Purchase #7 $62.93   8.608%   $68.347   $68.35   $68.35   $68.30  
  7 purchase totals = $1,049.00       $1,134.1485   $1,134.15   $1,134.15   $1,134.00