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 $87.74   9.631%   $96.1902   $96.19   $96.20   $96.20  
  Purchase #2 $52.90   13.859%   $60.2314   $60.23   $60.25   $60.20  
  Purchase #3 $193.93   6.647%   $206.8205   $206.82   $206.80   $206.80  
  Purchase #4 $244.83   5.116%   $257.3555   $257.36   $257.35   $257.40  
  Purchase #5 $122.34   8.748%   $133.0423   $133.04   $133.05   $133.00  
  Purchase #6 $162.58   10.259%   $179.2591   $179.26   $179.25   $179.30  
  Purchase #7 $233.39   11.113%   $259.3266   $259.33   $259.35   $259.30  
  7 purchase totals = $1,097.71       $1,192.2256   $1,192.23   $1,192.25   $1,192.20