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 $65.58   5.658%   $69.2905   $69.29   $69.30   $69.30  
  Purchase #2 $110.75   8.296%   $119.9378   $119.94   $119.95   $119.90  
  Purchase #3 $26.27   13.307%   $29.7657   $29.77   $29.75   $29.80  
  Purchase #4 $249.77   10.104%   $275.0068   $275.01   $275.00   $275.00  
  Purchase #5 $103.53   4.529%   $108.2189   $108.22   $108.20   $108.20  
  Purchase #6 $214.32   5.832%   $226.8191   $226.82   $226.80   $226.80  
  Purchase #7 $66.85   13.756%   $76.0459   $76.05   $76.05   $76.00  
  7 purchase totals = $837.07       $905.0847   $905.10   $905.05   $905.00