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	$238.95	12.422%	$268.6324	$268.63	$268.65	$268.60
Purchase #2	$42.38	9.229%	$46.2913	$46.29	$46.30	$46.30
Purchase #3	$52.94	3.709%	$54.9035	$54.90	$54.90	$54.90
Purchase #4	$42.47	8.301%	$45.9954	$46.00	$46.00	$46.00
Purchase #5	$158.87	9.424%	$173.8419	$173.84	$173.85	$173.80
Purchase #6	$196.42	5.749%	$207.7122	$207.71	$207.70	$207.70
Purchase #7	$72.75	7.683%	$78.3394	$78.34	$78.35	$78.30
7 purchase totals =	$804.78		$875.7161	$875.71	$875.75	$875.60