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 $244.41   7.504%   $262.7505   $262.75   $262.75   $262.80  
  Purchase #2 $226.68   5.531%   $239.2177   $239.22   $239.20   $239.20  
  Purchase #3 $147.80   8.471%   $160.3201   $160.32   $160.30   $160.30  
  Purchase #4 $17.45   12.239%   $19.5857   $19.59   $19.60   $19.60  
  Purchase #5 $30.69   3.870%   $31.8777   $31.88   $31.90   $31.90  
  Purchase #6 $105.85   5.279%   $111.4378   $111.44   $111.45   $111.40  
  Purchase #7 $92.64   6.272%   $98.4504   $98.45   $98.45   $98.50  
  7 purchase totals = $865.52       $923.6399   $923.65   $923.65   $923.70