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 $215.73   11.137%   $239.7559   $239.76   $239.75   $239.80  
  Purchase #2 $200.25   6.276%   $212.8177   $212.82   $212.80   $212.80  
  Purchase #3 $173.33   7.445%   $186.2344   $186.23   $186.25   $186.20  
  Purchase #4 $150.28   10.706%   $166.369   $166.37   $166.35   $166.40  
  Purchase #5 $97.77   5.120%   $102.7758   $102.78   $102.80   $102.80  
  Purchase #6 $13.94   11.192%   $15.5002   $15.50   $15.50   $15.50  
  Purchase #7 $16.49   3.295%   $17.0333   $17.03   $17.05   $17.00  
  7 purchase totals = $867.79       $940.4863   $940.49   $940.50   $940.50