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 $60.62   11.630%   $67.6701   $67.67   $67.65   $67.70  
  Purchase #2 $145.57   7.557%   $156.5707   $156.57   $156.55   $156.60  
  Purchase #3 $129.65   12.319%   $145.6216   $145.62   $145.60   $145.60  
  Purchase #4 $119.74   12.178%   $134.3219   $134.32   $134.30   $134.30  
  Purchase #5 $36.67   4.265%   $38.234   $38.23   $38.25   $38.20  
  Purchase #6 $24.76   7.411%   $26.595   $26.60   $26.60   $26.60  
  Purchase #7 $151.29   7.855%   $163.1738   $163.17   $163.15   $163.20  
  7 purchase totals = $668.30       $732.1871   $732.18   $732.10   $732.20