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 $205.54   8.649%   $223.3172   $223.32   $223.30   $223.30  
  Purchase #2 $78.42   10.354%   $86.5396   $86.54   $86.55   $86.50  
  Purchase #3 $227.81   10.158%   $250.9509   $250.95   $250.95   $251.00  
  Purchase #4 $133.97   9.194%   $146.2872   $146.29   $146.30   $146.30  
  Purchase #5 $108.35   5.747%   $114.5769   $114.58   $114.60   $114.60  
  Purchase #6 $233.87   9.667%   $256.4782   $256.48   $256.50   $256.50  
  Purchase #7 $71.99   5.399%   $75.8767   $75.88   $75.90   $75.90  
  7 purchase totals = $1,059.95       $1,154.0267   $1,154.04   $1,154.10   $1,154.10