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	$149.72	9.613%	$164.1126	$164.11	$164.10	$164.10
Purchase #2	$39.42	3.416%	$40.7666	$40.77	$40.75	$40.80
Purchase #3	$99.45	12.250%	$111.6326	$111.63	$111.65	$111.60
Purchase #4	$222.84	11.663%	$248.8298	$248.83	$248.85	$248.80
Purchase #5	$184.89	12.401%	$207.8182	$207.82	$207.80	$207.80
Purchase #6	$36.27	9.418%	$39.6859	$39.69	$39.70	$39.70
Purchase #7	$176.43	10.871%	$195.6097	$195.61	$195.60	$195.60
7 purchase totals =	$909.02		$1,008.4554	$1,008.46	$1,008.45	$1,008.40