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	$8.30	3.310%	$8.5747	$8.57	$8.55	$8.60
Purchase #2	$154.66	12.152%	$173.4543	$173.45	$173.45	$173.50
Purchase #3	$198.85	11.804%	$222.3223	$222.32	$222.30	$222.30
Purchase #4	$78.99	12.858%	$89.1465	$89.15	$89.15	$89.10
Purchase #5	$10.45	9.219%	$11.4134	$11.41	$11.40	$11.40
Purchase #6	$9.57	7.635%	$10.3007	$10.30	$10.30	$10.30
Purchase #7	$159.70	3.129%	$164.697	$164.70	$164.70	$164.70
7 purchase totals =	$620.52		$679.9089	$679.90	$679.85	$679.90