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 $248.89   3.232%   $256.9341   $256.93   $256.95   $256.90  
  Purchase #2 $22.94   5.789%   $24.268   $24.27   $24.25   $24.30  
  Purchase #3 $11.29   4.185%   $11.7625   $11.76   $11.75   $11.80  
  Purchase #4 $17.88   6.498%   $19.0418   $19.04   $19.05   $19.00  
  Purchase #5 $62.92   10.248%   $69.368   $69.37   $69.35   $69.40  
  Purchase #6 $128.54   13.658%   $146.096   $146.10   $146.10   $146.10  
  Purchase #7 $199.51   8.822%   $217.1108   $217.11   $217.10   $217.10  
  7 purchase totals = $691.97       $744.5812   $744.58   $744.55   $744.60