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	$235.49	3.389%	$243.4708	$243.47	$243.45	$243.50
Purchase #2	$72.85	7.690%	$78.4522	$78.45	$78.45	$78.50
Purchase #3	$172.42	9.839%	$189.3844	$189.38	$189.40	$189.40
Purchase #4	$11.77	8.472%	$12.7672	$12.77	$12.75	$12.80
Purchase #5	$87.96	10.740%	$97.4069	$97.41	$97.40	$97.40
Purchase #6	$114.61	10.815%	$127.0051	$127.01	$127.00	$127.00
Purchase #7	$104.62	5.713%	$110.5969	$110.60	$110.60	$110.60
7 purchase totals =	$799.72		$859.0835	$859.09	$859.05	$859.20