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 $233.29   13.269%   $264.2453   $264.25   $264.25   $264.20  
  Purchase #2 $181.55   7.777%   $195.6691   $195.67   $195.65   $195.70  
  Purchase #3 $176.68   13.313%   $200.2014   $200.20   $200.20   $200.20  
  Purchase #4 $79.84   12.256%   $89.6252   $89.63   $89.65   $89.60  
  Purchase #5 $224.80   10.113%   $247.534   $247.53   $247.55   $247.50  
  Purchase #6 $133.63   8.418%   $144.879   $144.88   $144.90   $144.90  
  Purchase #7 $214.49   7.142%   $229.8089   $229.81   $229.80   $229.80  
  7 purchase totals = $1,244.28       $1,371.9629   $1,371.97   $1,372.00   $1,371.90