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	$139.32	9.587%	$152.6766	$152.68	$152.70	$152.70
Purchase #2	$244.88	9.705%	$268.6456	$268.65	$268.65	$268.60
Purchase #3	$45.45	12.797%	$51.2662	$51.27	$51.25	$51.30
Purchase #4	$91.42	5.849%	$96.7672	$96.77	$96.75	$96.80
Purchase #5	$201.81	10.807%	$223.6196	$223.62	$223.60	$223.60
Purchase #6	$18.59	10.320%	$20.5085	$20.51	$20.50	$20.50
Purchase #7	$146.60	13.865%	$166.9261	$166.93	$166.95	$166.90
7 purchase totals =	$888.07		$980.4098	$980.43	$980.40	$980.40