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 $245.76   4.409%   $256.5956   $256.60   $256.60   $256.60  
  Purchase #2 $233.36   13.854%   $265.6897   $265.69   $265.70   $265.70  
  Purchase #3 $100.73   12.310%   $113.1299   $113.13   $113.15   $113.10  
  Purchase #4 $238.72   5.517%   $251.8902   $251.89   $251.90   $251.90  
  Purchase #5 $165.36   8.714%   $179.7695   $179.77   $179.75   $179.80  
  Purchase #6 $147.25   12.372%   $165.4678   $165.47   $165.45   $165.50  
  Purchase #7 $13.78   10.455%   $15.2207   $15.22   $15.20   $15.20  
  7 purchase totals = $1,144.96       $1,247.7634   $1,247.77   $1,247.75   $1,247.80