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	$206.40	11.528%	$230.1938	$230.19	$230.20	$230.20
Purchase #2	$249.92	8.261%	$270.5659	$270.57	$270.55	$270.60
Purchase #3	$216.42	11.178%	$240.6114	$240.61	$240.60	$240.60
Purchase #4	$59.42	8.158%	$64.2675	$64.27	$64.25	$64.30
Purchase #5	$11.89	3.201%	$12.2706	$12.27	$12.25	$12.30
Purchase #6	$127.73	12.647%	$143.884	$143.88	$143.90	$143.90
Purchase #7	$116.36	9.701%	$127.6481	$127.65	$127.65	$127.60
7 purchase totals =	$988.14		$1,089.4413	$1,089.44	$1,089.40	$1,089.50