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	$79.34	13.571%	$90.1072	$90.11	$90.10	$90.10
Purchase #2	$170.34	4.808%	$178.5299	$178.53	$178.55	$178.50
Purchase #3	$227.64	9.439%	$249.1269	$249.13	$249.15	$249.10
Purchase #4	$117.70	12.365%	$132.2536	$132.25	$132.25	$132.30
Purchase #5	$100.96	10.245%	$111.3034	$111.30	$111.30	$111.30
Purchase #6	$200.86	5.466%	$211.839	$211.84	$211.85	$211.80
Purchase #7	$72.99	7.120%	$78.1869	$78.19	$78.20	$78.20
7 purchase totals =	$969.83		$1,051.3469	$1,051.35	$1,051.40	$1,051.30