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 $184.80   11.106%   $205.3239   $205.32   $205.30   $205.30  
  Purchase #2 $101.82   12.247%   $114.2899   $114.29   $114.30   $114.30  
  Purchase #3 $162.99   12.471%   $183.3165   $183.32   $183.30   $183.30  
  Purchase #4 $85.47   6.474%   $91.0033   $91.00   $91.00   $91.00  
  Purchase #5 $82.69   3.665%   $85.7206   $85.72   $85.70   $85.70  
  Purchase #6 $130.86   13.122%   $148.0314   $148.03   $148.05   $148.00  
  Purchase #7 $182.51   13.202%   $206.605   $206.61   $206.60   $206.60  
  7 purchase totals = $931.14       $1,034.2906   $1,034.29   $1,034.25   $1,034.20