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	$148.63	12.103%	$166.6187	$166.62	$166.60	$166.60
Purchase #2	$121.32	6.108%	$128.7302	$128.73	$128.75	$128.70
Purchase #3	$204.27	3.846%	$212.1262	$212.13	$212.15	$212.10
Purchase #4	$48.33	3.127%	$49.8413	$49.84	$49.85	$49.80
Purchase #5	$28.38	13.226%	$32.1335	$32.13	$32.15	$32.10
Purchase #6	$113.95	12.260%	$127.9203	$127.92	$127.90	$127.90
Purchase #7	$91.53	5.178%	$96.2694	$96.27	$96.25	$96.30
7 purchase totals =	$756.41		$813.6396	$813.64	$813.65	$813.50