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	$233.76	10.744%	$258.8752	$258.88	$258.90	$258.90
Purchase #2	$235.92	10.112%	$259.7762	$259.78	$259.80	$259.80
Purchase #3	$22.43	4.588%	$23.4591	$23.46	$23.45	$23.50
Purchase #4	$72.93	5.809%	$77.1665	$77.17	$77.15	$77.20
Purchase #5	$153.43	3.381%	$158.6175	$158.62	$158.60	$158.60
Purchase #6	$76.33	3.151%	$78.7352	$78.74	$78.75	$78.70
Purchase #7	$117.93	7.841%	$127.1769	$127.18	$127.20	$127.20
7 purchase totals =	$912.73		$983.8066	$983.83	$983.85	$983.90