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 $222.75   8.310%   $241.2605   $241.26   $241.25   $241.30  
  Purchase #2 $120.98   13.678%   $137.5276   $137.53   $137.55   $137.50  
  Purchase #3 $62.87   7.718%   $67.7223   $67.72   $67.70   $67.70  
  Purchase #4 $188.47   6.173%   $200.1043   $200.10   $200.10   $200.10  
  Purchase #5 $214.96   13.794%   $244.6116   $244.61   $244.60   $244.60  
  Purchase #6 $118.41   6.342%   $125.9196   $125.92   $125.90   $125.90  
  Purchase #7 $250.47   7.112%   $268.2834   $268.28   $268.30   $268.30  
  7 purchase totals = $1,178.91       $1,285.4293   $1,285.42   $1,285.40   $1,285.40