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 $66.81   10.512%   $73.8331   $73.83   $73.85   $73.80  
  Purchase #2 $65.61   3.261%   $67.7495   $67.75   $67.75   $67.70  
  Purchase #3 $81.36   12.129%   $91.2282   $91.23   $91.25   $91.20  
  Purchase #4 $116.59   4.641%   $122.0009   $122.00   $122.00   $122.00  
  Purchase #5 $8.46   12.430%   $9.5116   $9.51   $9.50   $9.50  
  Purchase #6 $77.87   10.617%   $86.1375   $86.14   $86.15   $86.10  
  Purchase #7 $192.29   6.757%   $205.283   $205.28   $205.30   $205.30  
  7 purchase totals = $608.99       $655.7438   $655.74   $655.80   $655.60