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	$82.90	9.557%	$90.8228	$90.82	$90.80	$90.80
Purchase #2	$60.78	5.718%	$64.2554	$64.26	$64.25	$64.30
Purchase #3	$104.90	4.376%	$109.4904	$109.49	$109.50	$109.50
Purchase #4	$53.94	7.143%	$57.7929	$57.79	$57.80	$57.80
Purchase #5	$83.46	11.140%	$92.7574	$92.76	$92.75	$92.80
Purchase #6	$66.78	11.370%	$74.3729	$74.37	$74.35	$74.40
Purchase #7	$40.52	7.807%	$43.6834	$43.68	$43.70	$43.70
7 purchase totals =	$493.28		$533.1752	$533.17	$533.15	$533.30