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 $61.57   10.589%   $68.0896   $68.09   $68.10   $68.10  
  Purchase #2 $221.63   4.592%   $231.8072   $231.81   $231.80   $231.80  
  Purchase #3 $95.91   4.112%   $99.8538   $99.85   $99.85   $99.90  
  Purchase #4 $78.61   9.702%   $86.2367   $86.24   $86.25   $86.20  
  Purchase #5 $75.93   12.472%   $85.4   $85.40   $85.40   $85.40  
  Purchase #6 $52.36   5.186%   $55.0754   $55.08   $55.10   $55.10  
  Purchase #7 $196.96   9.382%   $215.4388   $215.44   $215.45   $215.40  
  7 purchase totals = $782.97       $841.9015   $841.91   $841.95   $841.90