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 $149.95   12.574%   $168.8047   $168.80   $168.80   $168.80  
  Purchase #2 $25.58   3.558%   $26.4901   $26.49   $26.50   $26.50  
  Purchase #3 $231.26   5.328%   $243.5815   $243.58   $243.60   $243.60  
  Purchase #4 $67.64   12.361%   $76.001   $76.00   $76.00   $76.00  
  Purchase #5 $245.90   9.769%   $269.922   $269.92   $269.90   $269.90  
  Purchase #6 $221.25   5.497%   $233.4121   $233.41   $233.40   $233.40  
  Purchase #7 $111.36   8.791%   $121.1497   $121.15   $121.15   $121.10  
  7 purchase totals = $1,052.94       $1,139.3611   $1,139.35   $1,139.35   $1,139.30