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	$42.99	12.380%	$48.3122	$48.31	$48.30	$48.30
Purchase #2	$131.74	4.740%	$137.9845	$137.98	$138.00	$138.00
Purchase #3	$75.39	6.454%	$80.2557	$80.26	$80.25	$80.30
Purchase #4	$101.86	9.139%	$111.169	$111.17	$111.15	$111.20
Purchase #5	$103.30	10.666%	$114.318	$114.32	$114.30	$114.30
Purchase #6	$207.72	10.258%	$229.0279	$229.03	$229.05	$229.00
Purchase #7	$192.68	9.380%	$210.7534	$210.75	$210.75	$210.80
7 purchase totals =	$855.68		$931.8207	$931.82	$931.80	$931.90