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	$207.50	13.550%	$235.6163	$235.62	$235.60	$235.60
Purchase #2	$85.53	4.145%	$89.0752	$89.08	$89.10	$89.10
Purchase #3	$78.83	12.386%	$88.5939	$88.59	$88.60	$88.60
Purchase #4	$98.48	5.745%	$104.1377	$104.14	$104.15	$104.10
Purchase #5	$137.64	5.392%	$145.0615	$145.06	$145.05	$145.10
Purchase #6	$20.39	9.427%	$22.3122	$22.31	$22.30	$22.30
Purchase #7	$101.30	13.206%	$114.6777	$114.68	$114.70	$114.70
7 purchase totals =	$729.67		$799.4745	$799.48	$799.50	$799.50