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	$156.38	3.105%	$161.2356	$161.24	$161.25	$161.20
Purchase #2	$65.69	8.343%	$71.1705	$71.17	$71.15	$71.20
Purchase #3	$58.64	4.830%	$61.4723	$61.47	$61.45	$61.50
Purchase #4	$162.80	13.578%	$184.905	$184.91	$184.90	$184.90
Purchase #5	$58.76	6.236%	$62.4243	$62.42	$62.40	$62.40
Purchase #6	$45.70	13.820%	$52.0157	$52.02	$52.00	$52.00
Purchase #7	$176.95	4.581%	$185.0561	$185.06	$185.05	$185.10
7 purchase totals =	$724.92		$778.2795	$778.29	$778.20	$778.30