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	$96.90	3.639%	$100.4262	$100.43	$100.45	$100.40
Purchase #2	$191.39	4.388%	$199.7882	$199.79	$199.80	$199.80
Purchase #3	$82.51	12.451%	$92.7833	$92.78	$92.80	$92.80
Purchase #4	$44.96	12.495%	$50.5778	$50.58	$50.60	$50.60
Purchase #5	$199.56	9.674%	$218.8654	$218.87	$218.85	$218.90
Purchase #6	$11.79	6.501%	$12.5565	$12.56	$12.55	$12.60
Purchase #7	$93.36	11.700%	$104.2831	$104.28	$104.30	$104.30
7 purchase totals =	$720.47		$779.2805	$779.29	$779.35	$779.40