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 $248.75   13.674%   $282.7641   $282.76   $282.75   $282.80  
  Purchase #2 $69.39   9.240%   $75.8016   $75.80   $75.80   $75.80  
  Purchase #3 $112.50   9.499%   $123.1864   $123.19   $123.20   $123.20  
  Purchase #4 $216.98   4.852%   $227.5079   $227.51   $227.50   $227.50  
  Purchase #5 $207.55   12.553%   $233.6038   $233.60   $233.60   $233.60  
  Purchase #6 $81.89   5.675%   $86.5373   $86.54   $86.55   $86.50  
  Purchase #7 $112.92   4.161%   $117.6186   $117.62   $117.60   $117.60  
  7 purchase totals = $1,049.98       $1,147.0197   $1,147.02   $1,147.00   $1,147.00