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 $61.73   10.597%   $68.2715   $68.27   $68.25   $68.30  
  Purchase #2 $200.53   12.524%   $225.6444   $225.64   $225.65   $225.60  
  Purchase #3 $152.37   9.361%   $166.6334   $166.63   $166.65   $166.60  
  Purchase #4 $17.37   9.803%   $19.0728   $19.07   $19.05   $19.10  
  Purchase #5 $25.58   3.552%   $26.4886   $26.49   $26.50   $26.50  
  Purchase #6 $163.53   3.230%   $168.812   $168.81   $168.80   $168.80  
  Purchase #7 $218.28   3.225%   $225.3195   $225.32   $225.30   $225.30  
  7 purchase totals = $839.39       $900.2422   $900.23   $900.20   $900.20