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 $244.80   6.320%   $260.2714   $260.27   $260.25   $260.30  
  Purchase #2 $85.43   9.113%   $93.2152   $93.22   $93.20   $93.20  
  Purchase #3 $165.85   13.541%   $188.3077   $188.31   $188.30   $188.30  
  Purchase #4 $208.87   8.533%   $226.6929   $226.69   $226.70   $226.70  
  Purchase #5 $242.87   12.807%   $273.9744   $273.97   $273.95   $274.00  
  Purchase #6 $217.42   13.381%   $246.513   $246.51   $246.50   $246.50  
  Purchase #7 $223.40   4.678%   $233.8507   $233.85   $233.85   $233.90  
  7 purchase totals = $1,388.64       $1,522.8253   $1,522.82   $1,522.75   $1,522.90