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	$13.60	10.356%	$15.0084	$15.01	$15.00	$15.00
Purchase #2	$56.31	8.521%	$61.1082	$61.11	$61.10	$61.10
Purchase #3	$214.77	7.808%	$231.5392	$231.54	$231.55	$231.50
Purchase #4	$74.49	10.799%	$82.5342	$82.53	$82.55	$82.50
Purchase #5	$46.94	7.718%	$50.5628	$50.56	$50.55	$50.60
Purchase #6	$226.25	10.712%	$250.4859	$250.49	$250.50	$250.50
Purchase #7	$190.78	13.476%	$216.4895	$216.49	$216.50	$216.50
7 purchase totals =	$823.14		$907.7282	$907.73	$907.75	$907.70