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 $62.25   3.247%   $64.2713   $64.27   $64.25   $64.30  
  Purchase #2 $230.27   7.110%   $246.6422   $246.64   $246.65   $246.60  
  Purchase #3 $125.93   6.605%   $134.2477   $134.25   $134.25   $134.20  
  Purchase #4 $83.67   5.116%   $87.9506   $87.95   $87.95   $88.00  
  Purchase #5 $77.66   11.183%   $86.3447   $86.34   $86.35   $86.30  
  Purchase #6 $28.74   4.747%   $30.1043   $30.10   $30.10   $30.10  
  Purchase #7 $59.85   11.837%   $66.9344   $66.93   $66.95   $66.90  
  7 purchase totals = $668.37       $716.4952   $716.48   $716.50   $716.40