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	$34.43	8.561%	$37.3776	$37.38	$37.40	$37.40
Purchase #2	$50.30	9.329%	$54.9925	$54.99	$55.00	$55.00
Purchase #3	$47.87	12.762%	$53.9792	$53.98	$54.00	$54.00
Purchase #4	$79.69	10.804%	$88.2997	$88.30	$88.30	$88.30
Purchase #5	$217.39	7.510%	$233.716	$233.72	$233.70	$233.70
Purchase #6	$99.86	11.443%	$111.287	$111.29	$111.30	$111.30
Purchase #7	$235.83	4.302%	$245.9754	$245.98	$246.00	$246.00
7 purchase totals =	$765.37		$825.6274	$825.64	$825.70	$825.70