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 $234.95   5.817%   $248.617   $248.62   $248.60   $248.60  
  Purchase #2 $94.38   5.161%   $99.251   $99.25   $99.25   $99.30  
  Purchase #3 $8.46   12.620%   $9.5277   $9.53   $9.55   $9.50  
  Purchase #4 $207.66   5.505%   $219.0917   $219.09   $219.10   $219.10  
  Purchase #5 $158.97   13.400%   $180.272   $180.27   $180.25   $180.30  
  Purchase #6 $82.81   9.332%   $90.5378   $90.54   $90.55   $90.50  
  Purchase #7 $86.40   8.162%   $93.452   $93.45   $93.45   $93.50  
  7 purchase totals = $873.63       $940.7492   $940.75   $940.75   $940.80