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 $162.63   8.688%   $176.7593   $176.76   $176.75   $176.80  
  Purchase #2 $62.39   8.233%   $67.5266   $67.53   $67.55   $67.50  
  Purchase #3 $187.28   3.686%   $194.1831   $194.18   $194.20   $194.20  
  Purchase #4 $165.71   8.367%   $179.575   $179.58   $179.60   $179.60  
  Purchase #5 $104.44   3.811%   $108.4202   $108.42   $108.40   $108.40  
  Purchase #6 $173.48   7.118%   $185.8283   $185.83   $185.85   $185.80  
  Purchase #7 $151.91   9.866%   $166.8974   $166.90   $166.90   $166.90  
  7 purchase totals = $1,007.84       $1,079.1899   $1,079.20   $1,079.25   $1,079.20