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 $227.52   11.468%   $253.612   $253.61   $253.60   $253.60  
  Purchase #2 $117.35   5.305%   $123.5754   $123.58   $123.60   $123.60  
  Purchase #3 $237.62   5.738%   $251.2546   $251.25   $251.25   $251.30  
  Purchase #4 $106.54   7.514%   $114.5454   $114.55   $114.55   $114.50  
  Purchase #5 $223.75   7.660%   $240.8893   $240.89   $240.90   $240.90  
  Purchase #6 $194.97   10.770%   $215.9683   $215.97   $215.95   $216.00  
  Purchase #7 $28.98   12.795%   $32.688   $32.69   $32.70   $32.70  
  7 purchase totals = $1,136.73       $1,232.5330   $1,232.54   $1,232.55   $1,232.60