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 $211.58   13.210%   $239.5297   $239.53   $239.55   $239.50  
  Purchase #2 $68.40   12.503%   $76.9521   $76.95   $76.95   $77.00  
  Purchase #3 $126.47   6.237%   $134.3579   $134.36   $134.35   $134.40  
  Purchase #4 $7.75   10.694%   $8.5788   $8.58   $8.60   $8.60  
  Purchase #5 $224.47   3.329%   $231.9426   $231.94   $231.95   $231.90  
  Purchase #6 $196.63   6.859%   $210.1169   $210.12   $210.10   $210.10  
  Purchase #7 $117.82   7.256%   $126.369   $126.37   $126.35   $126.40  
  7 purchase totals = $953.12       $1,027.8470   $1,027.85   $1,027.85   $1,027.90