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	$148.79	11.482%	$165.8741	$165.87	$165.85	$165.90
Purchase #2	$42.31	7.117%	$45.3212	$45.32	$45.30	$45.30
Purchase #3	$88.64	4.276%	$92.4302	$92.43	$92.45	$92.40
Purchase #4	$144.49	5.176%	$151.9688	$151.97	$151.95	$152.00
Purchase #5	$177.90	3.371%	$183.897	$183.90	$183.90	$183.90
Purchase #6	$78.48	7.403%	$84.2899	$84.29	$84.30	$84.30
Purchase #7	$238.97	6.661%	$254.8878	$254.89	$254.90	$254.90
7 purchase totals =	$919.58		$978.6690	$978.67	$978.65	$978.70