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 $239.97   7.219%   $257.2934   $257.29   $257.30   $257.30  
  Purchase #2 $105.93   13.753%   $120.4986   $120.50   $120.50   $120.50  
  Purchase #3 $64.63   10.189%   $71.2152   $71.22   $71.20   $71.20  
  Purchase #4 $118.47   9.641%   $129.8917   $129.89   $129.90   $129.90  
  Purchase #5 $186.70   6.314%   $198.4882   $198.49   $198.50   $198.50  
  Purchase #6 $233.96   8.176%   $253.0886   $253.09   $253.10   $253.10  
  Purchase #7 $61.70   5.165%   $64.8868   $64.89   $64.90   $64.90  
  7 purchase totals = $1,011.36       $1,095.3625   $1,095.37   $1,095.40   $1,095.40