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 $222.35   5.247%   $234.0167   $234.02   $234.00   $234.00  
  Purchase #2 $190.71   8.451%   $206.8269   $206.83   $206.85   $206.80  
  Purchase #3 $215.38   5.647%   $227.5425   $227.54   $227.55   $227.50  
  Purchase #4 $122.73   3.579%   $127.1225   $127.12   $127.10   $127.10  
  Purchase #5 $69.58   11.501%   $77.5824   $77.58   $77.60   $77.60  
  Purchase #6 $117.60   3.855%   $122.1335   $122.13   $122.15   $122.10  
  Purchase #7 $245.66   3.394%   $253.9977   $254.00   $254.00   $254.00  
  7 purchase totals = $1,184.01       $1,249.2222   $1,249.22   $1,249.25   $1,249.10