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	$19.47	6.289%	$20.6945	$20.69	$20.70	$20.70
Purchase #2	$230.91	3.564%	$239.1396	$239.14	$239.15	$239.10
Purchase #3	$134.40	6.702%	$143.4075	$143.41	$143.40	$143.40
Purchase #4	$53.61	10.519%	$59.2492	$59.25	$59.25	$59.20
Purchase #5	$209.49	11.270%	$233.0995	$233.10	$233.10	$233.10
Purchase #6	$91.55	10.563%	$101.2204	$101.22	$101.20	$101.20
Purchase #7	$12.76	6.592%	$13.6011	$13.60	$13.60	$13.60
7 purchase totals =	$752.19		$810.4118	$810.41	$810.40	$810.30