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 $96.59   5.335%   $101.7431   $101.74   $101.75   $101.70  
  Purchase #2 $212.86   8.169%   $230.2485   $230.25   $230.25   $230.20  
  Purchase #3 $16.70   8.238%   $18.0757   $18.08   $18.10   $18.10  
  Purchase #4 $92.40   9.588%   $101.2593   $101.26   $101.25   $101.30  
  Purchase #5 $139.27   8.766%   $151.4784   $151.48   $151.50   $151.50  
  Purchase #6 $60.74   4.165%   $63.2698   $63.27   $63.25   $63.30  
  Purchase #7 $125.74   5.161%   $132.2294   $132.23   $132.25   $132.20  
  7 purchase totals = $744.30       $798.3042   $798.31   $798.35   $798.30