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	$106.48	5.512%	$112.3492	$112.35	$112.35	$112.30
Purchase #2	$76.45	10.681%	$84.6156	$84.62	$84.60	$84.60
Purchase #3	$151.38	5.154%	$159.1821	$159.18	$159.20	$159.20
Purchase #4	$100.30	9.312%	$109.6399	$109.64	$109.65	$109.60
Purchase #5	$12.80	4.494%	$13.3752	$13.38	$13.40	$13.40
Purchase #6	$17.73	13.737%	$20.1656	$20.17	$20.15	$20.20
Purchase #7	$115.25	10.296%	$127.1161	$127.12	$127.10	$127.10
7 purchase totals =	$580.39		$626.4437	$626.46	$626.45	$626.40