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 $68.32   7.727%   $73.5991   $73.60   $73.60   $73.60  
  Purchase #2 $191.64   12.169%   $214.9607   $214.96   $214.95   $215.00  
  Purchase #3 $52.79   5.261%   $55.5673   $55.57   $55.55   $55.60  
  Purchase #4 $195.53   9.478%   $214.0623   $214.06   $214.05   $214.10  
  Purchase #5 $74.43   11.174%   $82.7468   $82.75   $82.75   $82.70  
  Purchase #6 $246.63   6.139%   $261.7706   $261.77   $261.75   $261.80  
  Purchase #7 $56.45   7.226%   $60.5291   $60.53   $60.55   $60.50  
  7 purchase totals = $885.79       $963.2359   $963.24   $963.20   $963.30