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	$55.55	3.585%	$57.5415	$57.54	$57.55	$57.50
Purchase #2	$195.31	9.598%	$214.0559	$214.06	$214.05	$214.10
Purchase #3	$169.28	13.476%	$192.0922	$192.09	$192.10	$192.10
Purchase #4	$190.48	3.370%	$196.8992	$196.90	$196.90	$196.90
Purchase #5	$120.69	13.694%	$137.2173	$137.22	$137.20	$137.20
Purchase #6	$219.68	3.408%	$227.1667	$227.17	$227.15	$227.20
Purchase #7	$51.55	7.657%	$55.4972	$55.50	$55.50	$55.50
7 purchase totals =	$1,002.54		$1,080.4700	$1,080.48	$1,080.45	$1,080.50