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	$20.88	3.317%	$21.5726	$21.57	$21.55	$21.60
Purchase #2	$194.39	6.211%	$206.4636	$206.46	$206.45	$206.50
Purchase #3	$180.95	4.858%	$189.7406	$189.74	$189.75	$189.70
Purchase #4	$38.43	10.592%	$42.5005	$42.50	$42.50	$42.50
Purchase #5	$96.71	3.785%	$100.3705	$100.37	$100.35	$100.40
Purchase #6	$66.88	5.553%	$70.5938	$70.59	$70.60	$70.60
Purchase #7	$205.38	7.342%	$220.459	$220.46	$220.45	$220.50
7 purchase totals =	$803.62		$851.7006	$851.69	$851.65	$851.80