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	$38.80	12.595%	$43.6869	$43.69	$43.70	$43.70
Purchase #2	$128.89	12.619%	$145.1546	$145.15	$145.15	$145.20
Purchase #3	$22.99	11.619%	$25.6612	$25.66	$25.65	$25.70
Purchase #4	$87.66	7.814%	$94.5098	$94.51	$94.50	$94.50
Purchase #5	$48.67	4.326%	$50.7755	$50.78	$50.80	$50.80
Purchase #6	$61.30	10.691%	$67.8536	$67.85	$67.85	$67.90
Purchase #7	$127.41	10.805%	$141.1767	$141.18	$141.20	$141.20
7 purchase totals =	$515.72		$568.8183	$568.82	$568.85	$569.00