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	$112.82	10.599%	$124.7778	$124.78	$124.80	$124.80
Purchase #2	$230.52	6.225%	$244.8699	$244.87	$244.85	$244.90
Purchase #3	$99.73	9.681%	$109.3849	$109.38	$109.40	$109.40
Purchase #4	$166.48	4.432%	$173.8584	$173.86	$173.85	$173.90
Purchase #5	$30.65	6.523%	$32.6493	$32.65	$32.65	$32.60
Purchase #6	$78.47	13.630%	$89.1655	$89.17	$89.15	$89.20
Purchase #7	$185.37	4.492%	$193.6968	$193.70	$193.70	$193.70
7 purchase totals =	$904.04		$968.4026	$968.41	$968.40	$968.50