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	$90.33	3.149%	$93.1745	$93.17	$93.15	$93.20
Purchase #2	$85.77	12.532%	$96.5187	$96.52	$96.50	$96.50
Purchase #3	$92.76	8.341%	$100.4971	$100.50	$100.50	$100.50
Purchase #4	$131.28	4.730%	$137.4895	$137.49	$137.50	$137.50
Purchase #5	$159.70	7.345%	$171.43	$171.43	$171.45	$171.40
Purchase #6	$43.39	13.149%	$49.0954	$49.10	$49.10	$49.10
Purchase #7	$176.58	12.514%	$198.6772	$198.68	$198.70	$198.70
7 purchase totals =	$779.81		$846.8824	$846.89	$846.90	$846.90