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	$241.55	5.600%	$255.0768	$255.08	$255.10	$255.10
Purchase #2	$50.96	8.774%	$55.4312	$55.43	$55.45	$55.40
Purchase #3	$33.58	10.685%	$37.168	$37.17	$37.15	$37.20
Purchase #4	$30.82	8.109%	$33.3192	$33.32	$33.30	$33.30
Purchase #5	$226.99	9.223%	$247.9253	$247.93	$247.95	$247.90
Purchase #6	$61.30	6.736%	$65.4292	$65.43	$65.45	$65.40
Purchase #7	$192.76	12.468%	$216.7933	$216.79	$216.80	$216.80
7 purchase totals =	$837.96		$911.1430	$911.15	$911.20	$911.10