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 $211.99   5.208%   $223.0304   $223.03   $223.05   $223.00  
  Purchase #2 $100.84   10.438%   $111.3657   $111.37   $111.35   $111.40  
  Purchase #3 $19.26   12.595%   $21.6858   $21.69   $21.70   $21.70  
  Purchase #4 $175.41   8.693%   $190.6584   $190.66   $190.65   $190.70  
  Purchase #5 $226.63   3.228%   $233.9456   $233.95   $233.95   $233.90  
  Purchase #6 $161.78   5.115%   $170.055   $170.06   $170.05   $170.10  
  Purchase #7 $62.90   12.465%   $70.7405   $70.74   $70.75   $70.70  
  7 purchase totals = $958.81       $1,021.4814   $1,021.50   $1,021.50   $1,021.50