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 $231.50   8.775%   $251.8141   $251.81   $251.80   $251.80  
  Purchase #2 $126.54   12.526%   $142.3904   $142.39   $142.40   $142.40  
  Purchase #3 $34.33   10.335%   $37.878   $37.88   $37.90   $37.90  
  Purchase #4 $124.41   6.711%   $132.7592   $132.76   $132.75   $132.80  
  Purchase #5 $21.90   5.271%   $23.0543   $23.05   $23.05   $23.10  
  Purchase #6 $169.64   13.160%   $191.9646   $191.96   $191.95   $192.00  
  Purchase #7 $190.51   9.157%   $207.955   $207.96   $207.95   $208.00  
  7 purchase totals = $898.83       $987.8156   $987.81   $987.80   $988.00