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	$116.53	10.276%	$128.5046	$128.50	$128.50	$128.50
Purchase #2	$223.67	10.197%	$246.4776	$246.48	$246.50	$246.50
Purchase #3	$92.41	8.748%	$100.494	$100.49	$100.50	$100.50
Purchase #4	$97.26	6.592%	$103.6714	$103.67	$103.65	$103.70
Purchase #5	$46.30	12.847%	$52.2482	$52.25	$52.25	$52.20
Purchase #6	$10.86	3.117%	$11.1985	$11.20	$11.20	$11.20
Purchase #7	$68.48	5.634%	$72.3382	$72.34	$72.35	$72.30
7 purchase totals =	$655.51		$714.9325	$714.93	$714.95	$714.90