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 $208.33   13.152%   $235.7296   $235.73   $235.75   $235.70  
  Purchase #2 $35.67   11.422%   $39.7442   $39.74   $39.75   $39.70  
  Purchase #3 $51.86   7.503%   $55.7511   $55.75   $55.75   $55.80  
  Purchase #4 $26.41   5.711%   $27.9183   $27.92   $27.90   $27.90  
  Purchase #5 $113.62   12.240%   $127.5271   $127.53   $127.55   $127.50  
  Purchase #6 $110.68   10.550%   $122.3567   $122.36   $122.35   $122.40  
  Purchase #7 $177.97   7.548%   $191.4032   $191.40   $191.40   $191.40  
  7 purchase totals = $724.54       $800.4302   $800.43   $800.45   $800.40