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 $52.86   12.710%   $59.5785   $59.58   $59.60   $59.60  
  Purchase #2 $233.75   13.868%   $266.1665   $266.17   $266.15   $266.20  
  Purchase #3 $174.92   10.384%   $193.0837   $193.08   $193.10   $193.10  
  Purchase #4 $194.97   11.141%   $216.6916   $216.69   $216.70   $216.70  
  Purchase #5 $101.92   4.694%   $106.7041   $106.70   $106.70   $106.70  
  Purchase #6 $214.60   12.773%   $242.0109   $242.01   $242.00   $242.00  
  Purchase #7 $242.97   7.695%   $261.6665   $261.67   $261.65   $261.70  
  7 purchase totals = $1,215.99       $1,345.9018   $1,345.90   $1,345.90   $1,346.00