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	$223.84	7.167%	$239.8826	$239.88	$239.90	$239.90
Purchase #2	$103.88	9.226%	$113.464	$113.46	$113.45	$113.50
Purchase #3	$170.40	10.749%	$188.7163	$188.72	$188.70	$188.70
Purchase #4	$192.49	9.173%	$210.1471	$210.15	$210.15	$210.10
Purchase #5	$122.68	4.434%	$128.1196	$128.12	$128.10	$128.10
Purchase #6	$54.97	8.313%	$59.5397	$59.54	$59.55	$59.50
Purchase #7	$39.27	11.194%	$43.6659	$43.67	$43.65	$43.70
7 purchase totals =	$907.53		$983.5352	$983.54	$983.50	$983.50