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	$36.27	3.185%	$37.4252	$37.43	$37.45	$37.40
Purchase #2	$153.47	8.630%	$166.7145	$166.71	$166.70	$166.70
Purchase #3	$146.78	13.651%	$166.8169	$166.82	$166.80	$166.80
Purchase #4	$97.83	8.565%	$106.2091	$106.21	$106.20	$106.20
Purchase #5	$189.97	4.608%	$198.7238	$198.72	$198.70	$198.70
Purchase #6	$75.61	9.851%	$83.0583	$83.06	$83.05	$83.10
Purchase #7	$117.37	8.629%	$127.4979	$127.50	$127.50	$127.50
7 purchase totals =	$817.30		$886.4457	$886.45	$886.40	$886.40