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 $61.88   9.388%   $67.6893   $67.69   $67.70   $67.70  
  Purchase #2 $239.55   13.588%   $272.1001   $272.10   $272.10   $272.10  
  Purchase #3 $91.29   11.325%   $101.6286   $101.63   $101.65   $101.60  
  Purchase #4 $193.34   8.329%   $209.4433   $209.44   $209.45   $209.40  
  Purchase #5 $210.71   11.273%   $234.4633   $234.46   $234.45   $234.50  
  Purchase #6 $62.71   11.553%   $69.9549   $69.95   $69.95   $70.00  
  Purchase #7 $127.67   13.262%   $144.6016   $144.60   $144.60   $144.60  
  7 purchase totals = $987.15       $1,099.8811   $1,099.87   $1,099.90   $1,099.90