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 $246.83   10.684%   $273.2013   $273.20   $273.20   $273.20  
  Purchase #2 $233.30   12.284%   $261.9586   $261.96   $261.95   $262.00  
  Purchase #3 $50.36   3.742%   $52.2445   $52.24   $52.25   $52.20  
  Purchase #4 $205.55   13.122%   $232.5223   $232.52   $232.50   $232.50  
  Purchase #5 $150.39   6.473%   $160.1247   $160.12   $160.10   $160.10  
  Purchase #6 $116.54   9.335%   $127.419   $127.42   $127.40   $127.40  
  Purchase #7 $193.76   7.232%   $207.7727   $207.77   $207.75   $207.80  
  7 purchase totals = $1,196.73       $1,315.2431   $1,315.23   $1,315.15   $1,315.20