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	$18.48	11.730%	$20.6477	$20.65	$20.65	$20.60
Purchase #2	$62.59	6.206%	$66.4743	$66.47	$66.45	$66.50
Purchase #3	$62.38	7.811%	$67.2525	$67.25	$67.25	$67.30
Purchase #4	$230.43	11.810%	$257.6438	$257.64	$257.65	$257.60
Purchase #5	$207.88	13.412%	$235.7609	$235.76	$235.75	$235.80
Purchase #6	$93.31	10.695%	$103.2895	$103.29	$103.30	$103.30
Purchase #7	$228.75	13.816%	$260.3541	$260.35	$260.35	$260.40
7 purchase totals =	$903.82		$1,011.4228	$1,011.41	$1,011.40	$1,011.50