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	$78.28	6.806%	$83.6077	$83.61	$83.60	$83.60
Purchase #2	$144.76	12.340%	$162.6234	$162.62	$162.60	$162.60
Purchase #3	$185.59	13.777%	$211.1587	$211.16	$211.15	$211.20
Purchase #4	$41.53	11.634%	$46.3616	$46.36	$46.35	$46.40
Purchase #5	$19.94	12.441%	$22.4207	$22.42	$22.40	$22.40
Purchase #6	$30.74	3.734%	$31.8878	$31.89	$31.90	$31.90
Purchase #7	$165.37	6.733%	$176.5044	$176.50	$176.50	$176.50
7 purchase totals =	$666.21		$734.5643	$734.56	$734.50	$734.60