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 $62.45   8.784%   $67.9356   $67.94   $67.95   $67.90  
  Purchase #2 $115.59   11.102%   $128.4228   $128.42   $128.40   $128.40  
  Purchase #3 $191.83   11.416%   $213.7293   $213.73   $213.75   $213.70  
  Purchase #4 $185.46   12.453%   $208.5553   $208.56   $208.55   $208.60  
  Purchase #5 $15.57   13.709%   $17.7045   $17.70   $17.70   $17.70  
  Purchase #6 $219.92   13.249%   $249.0572   $249.06   $249.05   $249.10  
  Purchase #7 $8.92   7.791%   $9.615   $9.62   $9.60   $9.60  
  7 purchase totals = $799.74       $895.0197   $895.03   $895.00   $895.00