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	$112.92	6.808%	$120.6076	$120.61	$120.60	$120.60
Purchase #2	$218.29	12.286%	$245.1091	$245.11	$245.10	$245.10
Purchase #3	$136.60	10.637%	$151.1301	$151.13	$151.15	$151.10
Purchase #4	$191.25	13.786%	$217.6157	$217.62	$217.60	$217.60
Purchase #5	$65.76	10.609%	$72.7365	$72.74	$72.75	$72.70
Purchase #6	$233.45	3.853%	$242.4448	$242.44	$242.45	$242.40
Purchase #7	$214.71	12.197%	$240.8982	$240.90	$240.90	$240.90
7 purchase totals =	$1,172.98		$1,290.5420	$1,290.55	$1,290.55	$1,290.40