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	$105.83	3.491%	$109.5245	$109.52	$109.50	$109.50
Purchase #2	$190.47	4.684%	$199.3916	$199.39	$199.40	$199.40
Purchase #3	$184.55	13.488%	$209.4421	$209.44	$209.45	$209.40
Purchase #4	$76.33	10.343%	$84.2248	$84.22	$84.20	$84.20
Purchase #5	$151.53	9.658%	$166.1648	$166.16	$166.15	$166.20
Purchase #6	$54.99	4.148%	$57.271	$57.27	$57.25	$57.30
Purchase #7	$42.96	6.188%	$45.6184	$45.62	$45.60	$45.60
7 purchase totals =	$806.66		$871.6372	$871.62	$871.55	$871.60