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	$40.92	10.219%	$45.1016	$45.10	$45.10	$45.10
Purchase #2	$113.47	6.223%	$120.5312	$120.53	$120.55	$120.50
Purchase #3	$98.41	13.728%	$111.9197	$111.92	$111.90	$111.90
Purchase #4	$148.99	4.485%	$155.6722	$155.67	$155.65	$155.70
Purchase #5	$227.80	12.739%	$256.8194	$256.82	$256.80	$256.80
Purchase #6	$113.29	8.857%	$123.3241	$123.32	$123.30	$123.30
Purchase #7	$103.49	7.837%	$111.6005	$111.60	$111.60	$111.60
7 purchase totals =	$846.37		$924.9687	$924.96	$924.90	$924.90