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	$121.49	8.110%	$131.3428	$131.34	$131.35	$131.30
Purchase #2	$107.57	3.861%	$111.7233	$111.72	$111.70	$111.70
Purchase #3	$41.74	4.261%	$43.5185	$43.52	$43.50	$43.50
Purchase #4	$179.49	3.827%	$186.3591	$186.36	$186.35	$186.40
Purchase #5	$10.30	6.279%	$10.9467	$10.95	$10.95	$10.90
Purchase #6	$229.56	12.533%	$258.3308	$258.33	$258.35	$258.30
Purchase #7	$149.83	5.739%	$158.4287	$158.43	$158.45	$158.40
7 purchase totals =	$839.98		$900.6499	$900.65	$900.65	$900.50