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 $196.97   3.689%   $204.2362   $204.24   $204.25   $204.20  
  Purchase #2 $231.49   6.569%   $246.6966   $246.70   $246.70   $246.70  
  Purchase #3 $174.98   11.771%   $195.5769   $195.58   $195.60   $195.60  
  Purchase #4 $60.62   4.242%   $63.1915   $63.19   $63.20   $63.20  
  Purchase #5 $147.30   13.211%   $166.7598   $166.76   $166.75   $166.80  
  Purchase #6 $218.69   7.381%   $234.8315   $234.83   $234.85   $234.80  
  Purchase #7 $153.49   6.772%   $163.8843   $163.88   $163.90   $163.90  
  7 purchase totals = $1,183.54       $1,275.1768   $1,275.18   $1,275.25   $1,275.20