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	$102.74	13.670%	$116.7846	$116.78	$116.80	$116.80
Purchase #2	$90.83	10.581%	$100.4407	$100.44	$100.45	$100.40
Purchase #3	$96.38	13.680%	$109.5648	$109.56	$109.55	$109.60
Purchase #4	$156.86	6.530%	$167.103	$167.10	$167.10	$167.10
Purchase #5	$92.84	9.128%	$101.3144	$101.31	$101.30	$101.30
Purchase #6	$111.81	13.830%	$127.2733	$127.27	$127.25	$127.30
Purchase #7	$117.44	12.190%	$131.7559	$131.76	$131.75	$131.80
7 purchase totals =	$768.90		$854.2367	$854.22	$854.20	$854.30