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 $190.33   13.512%   $216.0474   $216.05   $216.05   $216.00  
  Purchase #2 $184.74   11.731%   $206.4118   $206.41   $206.40   $206.40  
  Purchase #3 $47.47   12.293%   $53.3055   $53.31   $53.30   $53.30  
  Purchase #4 $218.78   13.671%   $248.6894   $248.69   $248.70   $248.70  
  Purchase #5 $187.53   5.301%   $197.471   $197.47   $197.45   $197.50  
  Purchase #6 $234.91   10.118%   $258.6782   $258.68   $258.70   $258.70  
  Purchase #7 $14.76   9.729%   $16.196   $16.20   $16.20   $16.20  
  7 purchase totals = $1,078.52       $1,196.7993   $1,196.81   $1,196.80   $1,196.80