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 $194.70   8.496%   $211.2417   $211.24   $211.25   $211.20  
  Purchase #2 $104.37   10.113%   $114.9249   $114.92   $114.90   $114.90  
  Purchase #3 $222.56   6.358%   $236.7104   $236.71   $236.70   $236.70  
  Purchase #4 $94.51   4.599%   $98.8565   $98.86   $98.85   $98.90  
  Purchase #5 $230.96   11.628%   $257.816   $257.82   $257.80   $257.80  
  Purchase #6 $233.89   6.573%   $249.2636   $249.26   $249.25   $249.30  
  Purchase #7 $214.48   8.272%   $232.2218   $232.22   $232.20   $232.20  
  7 purchase totals = $1,295.47       $1,401.0349   $1,401.03   $1,400.95   $1,401.00