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	$212.37	12.471%	$238.8547	$238.85	$238.85	$238.90
Purchase #2	$127.69	13.472%	$144.8924	$144.89	$144.90	$144.90
Purchase #3	$189.48	11.665%	$211.5828	$211.58	$211.60	$211.60
Purchase #4	$35.90	5.213%	$37.7715	$37.77	$37.75	$37.80
Purchase #5	$16.77	13.676%	$19.0635	$19.06	$19.05	$19.10
Purchase #6	$230.62	6.565%	$245.7602	$245.76	$245.75	$245.80
Purchase #7	$78.43	3.674%	$81.3115	$81.31	$81.30	$81.30
7 purchase totals =	$891.26		$979.2366	$979.22	$979.20	$979.40