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	$16.46	11.718%	$18.3888	$18.39	$18.40	$18.40
Purchase #2	$53.47	8.574%	$58.0545	$58.05	$58.05	$58.10
Purchase #3	$96.29	3.104%	$99.2788	$99.28	$99.30	$99.30
Purchase #4	$100.81	6.196%	$107.0562	$107.06	$107.05	$107.10
Purchase #5	$147.97	12.340%	$166.2295	$166.23	$166.25	$166.20
Purchase #6	$41.88	13.190%	$47.404	$47.40	$47.40	$47.40
Purchase #7	$114.39	11.256%	$127.2657	$127.27	$127.25	$127.30
7 purchase totals =	$571.27		$623.6775	$623.68	$623.70	$623.80