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	$235.95	3.526%	$244.2696	$244.27	$244.25	$244.30
Purchase #2	$222.58	4.413%	$232.4025	$232.40	$232.40	$232.40
Purchase #3	$151.69	13.106%	$171.5705	$171.57	$171.55	$171.60
Purchase #4	$250.98	10.707%	$277.8524	$277.85	$277.85	$277.90
Purchase #5	$104.73	6.731%	$111.7794	$111.78	$111.80	$111.80
Purchase #6	$25.38	9.784%	$27.8632	$27.86	$27.85	$27.90
Purchase #7	$230.25	10.751%	$255.0042	$255.00	$255.00	$255.00
7 purchase totals =	$1,221.56		$1,320.7418	$1,320.73	$1,320.70	$1,320.90