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 $154.86   8.325%   $167.7521   $167.75   $167.75   $167.80  
  Purchase #2 $24.39   7.255%   $26.1595   $26.16   $26.15   $26.20  
  Purchase #3 $222.47   11.784%   $248.6859   $248.69   $248.70   $248.70  
  Purchase #4 $128.78   12.408%   $144.759   $144.76   $144.75   $144.80  
  Purchase #5 $214.93   11.206%   $239.0151   $239.02   $239.00   $239.00  
  Purchase #6 $66.95   5.324%   $70.5144   $70.51   $70.50   $70.50  
  Purchase #7 $157.88   6.652%   $168.3822   $168.38   $168.40   $168.40  
  7 purchase totals = $970.26       $1,065.2682   $1,065.27   $1,065.25   $1,065.40