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	$59.31	11.131%	$65.9118	$65.91	$65.90	$65.90
Purchase #2	$72.45	13.532%	$82.2539	$82.25	$82.25	$82.30
Purchase #3	$225.86	10.828%	$250.3161	$250.32	$250.30	$250.30
Purchase #4	$247.58	6.722%	$264.2223	$264.22	$264.20	$264.20
Purchase #5	$177.80	9.286%	$194.3105	$194.31	$194.30	$194.30
Purchase #6	$169.67	9.451%	$185.7055	$185.71	$185.70	$185.70
Purchase #7	$221.27	13.729%	$251.6482	$251.65	$251.65	$251.60
7 purchase totals =	$1,173.94		$1,294.3683	$1,294.37	$1,294.30	$1,294.30