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	$223.31	3.284%	$230.6435	$230.64	$230.65	$230.60
Purchase #2	$238.30	7.783%	$256.8469	$256.85	$256.85	$256.80
Purchase #3	$234.76	11.799%	$262.4593	$262.46	$262.45	$262.50
Purchase #4	$238.45	6.809%	$254.6861	$254.69	$254.70	$254.70
Purchase #5	$174.40	5.650%	$184.2536	$184.25	$184.25	$184.30
Purchase #6	$71.92	8.805%	$78.2526	$78.25	$78.25	$78.30
Purchase #7	$24.92	5.424%	$26.2717	$26.27	$26.25	$26.30
7 purchase totals =	$1,206.06		$1,293.4137	$1,293.41	$1,293.40	$1,293.50