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	$52.55	3.594%	$54.4386	$54.44	$54.45	$54.40
Purchase #2	$127.92	9.848%	$140.5176	$140.52	$140.50	$140.50
Purchase #3	$12.66	8.632%	$13.7528	$13.75	$13.75	$13.80
Purchase #4	$51.52	11.369%	$57.3773	$57.38	$57.40	$57.40
Purchase #5	$100.73	10.602%	$111.4094	$111.41	$111.40	$111.40
Purchase #6	$78.58	9.436%	$85.9948	$85.99	$86.00	$86.00
Purchase #7	$159.35	7.397%	$171.1371	$171.14	$171.15	$171.10
7 purchase totals =	$583.31		$634.6276	$634.63	$634.65	$634.60