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	$59.66	4.277%	$62.2117	$62.21	$62.20	$62.20
Purchase #2	$145.61	13.754%	$165.6372	$165.64	$165.65	$165.60
Purchase #3	$39.64	8.718%	$43.0958	$43.10	$43.10	$43.10
Purchase #4	$193.71	9.728%	$212.5541	$212.55	$212.55	$212.60
Purchase #5	$68.91	10.498%	$76.1442	$76.14	$76.15	$76.10
Purchase #6	$41.91	13.348%	$47.5041	$47.50	$47.50	$47.50
Purchase #7	$28.28	13.153%	$31.9997	$32.00	$32.00	$32.00
7 purchase totals =	$577.72		$639.1468	$639.14	$639.15	$639.10