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 $224.78   3.654%   $232.9935   $232.99   $233.00   $233.00  
  Purchase #2 $76.39   8.589%   $82.9511   $82.95   $82.95   $83.00  
  Purchase #3 $95.92   10.758%   $106.2391   $106.24   $106.25   $106.20  
  Purchase #4 $164.77   7.244%   $176.7059   $176.71   $176.70   $176.70  
  Purchase #5 $89.88   10.299%   $99.1367   $99.14   $99.15   $99.10  
  Purchase #6 $180.55   6.848%   $192.9141   $192.91   $192.90   $192.90  
  Purchase #7 $122.42   3.159%   $126.2872   $126.29   $126.30   $126.30  
  7 purchase totals = $954.71       $1,017.2276   $1,017.23   $1,017.25   $1,017.20