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	$27.41	3.281%	$28.3093	$28.31	$28.30	$28.30
Purchase #2	$233.57	10.614%	$258.3611	$258.36	$258.35	$258.40
Purchase #3	$17.48	10.464%	$19.3091	$19.31	$19.30	$19.30
Purchase #4	$49.72	7.149%	$53.2745	$53.27	$53.25	$53.30
Purchase #5	$222.88	4.861%	$233.7142	$233.71	$233.70	$233.70
Purchase #6	$148.62	4.604%	$155.4625	$155.46	$155.45	$155.50
Purchase #7	$50.83	11.437%	$56.6434	$56.64	$56.65	$56.60
7 purchase totals =	$750.51		$805.0741	$805.06	$805.00	$805.10