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 $240.33   11.328%   $267.5546   $267.55   $267.55   $267.60  
  Purchase #2 $89.79   7.643%   $96.6526   $96.65   $96.65   $96.70  
  Purchase #3 $159.40   10.465%   $176.0812   $176.08   $176.10   $176.10  
  Purchase #4 $32.36   3.196%   $33.3942   $33.39   $33.40   $33.40  
  Purchase #5 $162.86   7.141%   $174.4898   $174.49   $174.50   $174.50  
  Purchase #6 $20.36   13.259%   $23.0595   $23.06   $23.05   $23.10  
  Purchase #7 $68.49   7.635%   $73.7192   $73.72   $73.70   $73.70  
  7 purchase totals = $773.59       $844.9511   $844.94   $844.95   $845.10