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 $108.64   10.169%   $119.6876   $119.69   $119.70   $119.70  
  Purchase #2 $156.33   12.565%   $175.9729   $175.97   $175.95   $176.00  
  Purchase #3 $91.66   3.353%   $94.7334   $94.73   $94.75   $94.70  
  Purchase #4 $112.97   5.717%   $119.4285   $119.43   $119.45   $119.40  
  Purchase #5 $96.76   8.416%   $104.9033   $104.90   $104.90   $104.90  
  Purchase #6 $142.90   3.530%   $147.9444   $147.94   $147.95   $147.90  
  Purchase #7 $94.68   11.470%   $105.5398   $105.54   $105.55   $105.50  
  7 purchase totals = $803.94       $868.2099   $868.20   $868.25   $868.10