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	$39.39	8.412%	$42.7035	$42.70	$42.70	$42.70
Purchase #2	$54.48	9.718%	$59.7744	$59.77	$59.75	$59.80
Purchase #3	$43.72	6.214%	$46.4368	$46.44	$46.45	$46.40
Purchase #4	$206.52	10.103%	$227.3847	$227.38	$227.40	$227.40
Purchase #5	$213.92	9.136%	$233.4637	$233.46	$233.45	$233.50
Purchase #6	$103.64	7.383%	$111.2917	$111.29	$111.30	$111.30
Purchase #7	$7.44	9.114%	$8.1181	$8.12	$8.10	$8.10
7 purchase totals =	$669.11		$729.1729	$729.16	$729.15	$729.20