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 $144.43   12.766%   $162.8679   $162.87   $162.85   $162.90  
  Purchase #2 $160.71   10.760%   $178.0024   $178.00   $178.00   $178.00  
  Purchase #3 $207.67   3.860%   $215.6861   $215.69   $215.70   $215.70  
  Purchase #4 $170.25   3.386%   $176.0147   $176.01   $176.00   $176.00  
  Purchase #5 $71.49   10.712%   $79.148   $79.15   $79.15   $79.10  
  Purchase #6 $231.61   3.581%   $239.904   $239.90   $239.90   $239.90  
  Purchase #7 $133.70   12.198%   $150.0087   $150.01   $150.00   $150.00  
  7 purchase totals = $1,119.86       $1,201.6318   $1,201.63   $1,201.60   $1,201.60