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 $217.52   13.540%   $246.9722   $246.97   $246.95   $247.00  
  Purchase #2 $137.46   4.326%   $143.4065   $143.41   $143.40   $143.40  
  Purchase #3 $88.35   11.311%   $98.3433   $98.34   $98.35   $98.30  
  Purchase #4 $198.69   3.335%   $205.3163   $205.32   $205.30   $205.30  
  Purchase #5 $158.52   7.554%   $170.4946   $170.49   $170.50   $170.50  
  Purchase #6 $137.25   4.606%   $143.5717   $143.57   $143.55   $143.60  
  Purchase #7 $23.95   7.188%   $25.6715   $25.67   $25.65   $25.70  
  7 purchase totals = $961.74       $1,033.7761   $1,033.77   $1,033.70   $1,033.80