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	$80.72	10.428%	$89.1375	$89.14	$89.15	$89.10
Purchase #2	$231.93	11.595%	$258.8223	$258.82	$258.80	$258.80
Purchase #3	$21.68	6.717%	$23.1362	$23.14	$23.15	$23.10
Purchase #4	$73.81	11.535%	$82.324	$82.32	$82.30	$82.30
Purchase #5	$167.60	10.760%	$185.6338	$185.63	$185.65	$185.60
Purchase #6	$107.68	10.669%	$119.1684	$119.17	$119.15	$119.20
Purchase #7	$247.85	5.110%	$260.5151	$260.52	$260.50	$260.50
7 purchase totals =	$931.27		$1,018.7373	$1,018.74	$1,018.70	$1,018.60