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	$20.64	8.279%	$22.3488	$22.35	$22.35	$22.30
Purchase #2	$86.57	3.792%	$89.8527	$89.85	$89.85	$89.90
Purchase #3	$62.49	7.705%	$67.3049	$67.30	$67.30	$67.30
Purchase #4	$98.89	12.724%	$111.4728	$111.47	$111.45	$111.50
Purchase #5	$157.93	4.599%	$165.1932	$165.19	$165.20	$165.20
Purchase #6	$9.93	10.243%	$10.9471	$10.95	$10.95	$10.90
Purchase #7	$55.55	11.290%	$61.8216	$61.82	$61.80	$61.80
7 purchase totals =	$492.00		$528.9411	$528.93	$528.90	$528.90