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 $217.35   13.458%   $246.601   $246.60   $246.60   $246.60  
  Purchase #2 $189.99   13.511%   $215.6595   $215.66   $215.65   $215.70  
  Purchase #3 $22.88   5.670%   $24.1773   $24.18   $24.20   $24.20  
  Purchase #4 $53.94   5.838%   $57.089   $57.09   $57.10   $57.10  
  Purchase #5 $169.27   9.503%   $185.3557   $185.36   $185.35   $185.40  
  Purchase #6 $23.75   11.151%   $26.3984   $26.40   $26.40   $26.40  
  Purchase #7 $193.27   10.582%   $213.7218   $213.72   $213.70   $213.70  
  7 purchase totals = $870.45       $969.0027   $969.01   $969.00   $969.10