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 $56.89   13.685%   $64.6754   $64.68   $64.70   $64.70  
  Purchase #2 $32.80   7.194%   $35.1596   $35.16   $35.15   $35.20  
  Purchase #3 $240.58   5.552%   $253.937   $253.94   $253.95   $253.90  
  Purchase #4 $223.95   10.630%   $247.7559   $247.76   $247.75   $247.80  
  Purchase #5 $73.37   8.762%   $79.7987   $79.80   $79.80   $79.80  
  Purchase #6 $65.37   12.426%   $73.4929   $73.49   $73.50   $73.50  
  Purchase #7 $199.85   6.704%   $213.2479   $213.25   $213.25   $213.20  
  7 purchase totals = $892.81       $968.0674   $968.08   $968.10   $968.10