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 $245.84   9.720%   $269.7356   $269.74   $269.75   $269.70  
  Purchase #2 $177.29   8.561%   $192.4678   $192.47   $192.45   $192.50  
  Purchase #3 $110.42   3.229%   $113.9855   $113.99   $114.00   $114.00  
  Purchase #4 $126.37   6.146%   $134.1367   $134.14   $134.15   $134.10  
  Purchase #5 $190.42   12.545%   $214.3082   $214.31   $214.30   $214.30  
  Purchase #6 $49.31   9.649%   $54.0679   $54.07   $54.05   $54.10  
  Purchase #7 $65.70   12.436%   $73.8705   $73.87   $73.85   $73.90  
  7 purchase totals = $965.35       $1,052.5722   $1,052.59   $1,052.55   $1,052.60