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	$227.59	10.546%	$251.5916	$251.59	$251.60	$251.60
Purchase #2	$111.45	4.633%	$116.6135	$116.61	$116.60	$116.60
Purchase #3	$73.53	9.643%	$80.6205	$80.62	$80.60	$80.60
Purchase #4	$13.92	12.565%	$15.669	$15.67	$15.65	$15.70
Purchase #5	$135.97	11.471%	$151.5671	$151.57	$151.55	$151.60
Purchase #6	$53.30	4.347%	$55.617	$55.62	$55.60	$55.60
Purchase #7	$223.93	9.366%	$244.9033	$244.90	$244.90	$244.90
7 purchase totals =	$839.69		$916.5820	$916.58	$916.50	$916.60