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	$159.61	4.369%	$166.5834	$166.58	$166.60	$166.60
Purchase #2	$137.31	12.535%	$154.5218	$154.52	$154.50	$154.50
Purchase #3	$105.79	5.387%	$111.4889	$111.49	$111.50	$111.50
Purchase #4	$216.63	13.537%	$245.9552	$245.96	$245.95	$246.00
Purchase #5	$39.72	9.541%	$43.5097	$43.51	$43.50	$43.50
Purchase #6	$40.47	9.461%	$44.2989	$44.30	$44.30	$44.30
Purchase #7	$40.74	6.532%	$43.4011	$43.40	$43.40	$43.40
7 purchase totals =	$740.27		$809.7590	$809.76	$809.75	$809.80