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	$52.82	3.262%	$54.543	$54.54	$54.55	$54.50
Purchase #2	$148.53	5.491%	$156.6858	$156.69	$156.70	$156.70
Purchase #3	$21.72	12.806%	$24.5015	$24.50	$24.50	$24.50
Purchase #4	$101.99	9.294%	$111.469	$111.47	$111.45	$111.50
Purchase #5	$223.28	11.369%	$248.6647	$248.66	$248.65	$248.70
Purchase #6	$72.87	13.740%	$82.8823	$82.88	$82.90	$82.90
Purchase #7	$120.92	6.515%	$128.7979	$128.80	$128.80	$128.80
7 purchase totals =	$742.13		$807.5442	$807.54	$807.55	$807.60