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 $76.91   10.754%   $85.1809   $85.18   $85.20   $85.20  
  Purchase #2 $110.91   9.461%   $121.4032   $121.40   $121.40   $121.40  
  Purchase #3 $168.96   3.846%   $175.4582   $175.46   $175.45   $175.50  
  Purchase #4 $49.99   13.748%   $56.8626   $56.86   $56.85   $56.90  
  Purchase #5 $220.68   13.172%   $249.748   $249.75   $249.75   $249.70  
  Purchase #6 $155.83   4.492%   $162.8299   $162.83   $162.85   $162.80  
  Purchase #7 $200.48   7.692%   $215.9009   $215.90   $215.90   $215.90  
  7 purchase totals = $983.76       $1,067.3837   $1,067.38   $1,067.40   $1,067.40