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 $92.76   6.243%   $98.551   $98.55   $98.55   $98.60  
  Purchase #2 $186.84   4.681%   $195.586   $195.59   $195.60   $195.60  
  Purchase #3 $121.50   4.274%   $126.6929   $126.69   $126.70   $126.70  
  Purchase #4 $85.76   12.368%   $96.3668   $96.37   $96.35   $96.40  
  Purchase #5 $57.97   9.663%   $63.5716   $63.57   $63.55   $63.60  
  Purchase #6 $148.83   9.139%   $162.4316   $162.43   $162.45   $162.40  
  Purchase #7 $70.99   8.726%   $77.1846   $77.18   $77.20   $77.20  
  7 purchase totals = $764.65       $820.3845   $820.38   $820.40   $820.50