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	$40.64	4.451%	$42.4489	$42.45	$42.45	$42.40
Purchase #2	$153.58	12.368%	$172.5748	$172.57	$172.55	$172.60
Purchase #3	$36.73	10.608%	$40.6263	$40.63	$40.65	$40.60
Purchase #4	$101.99	12.588%	$114.8285	$114.83	$114.85	$114.80
Purchase #5	$86.37	9.563%	$94.6296	$94.63	$94.65	$94.60
Purchase #6	$179.83	10.283%	$198.3219	$198.32	$198.30	$198.30
Purchase #7	$131.71	10.232%	$145.1866	$145.19	$145.20	$145.20
7 purchase totals =	$730.85		$808.6166	$808.62	$808.65	$808.50