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	$103.27	12.661%	$116.345	$116.35	$116.35	$116.30
Purchase #2	$122.96	7.673%	$132.3947	$132.39	$132.40	$132.40
Purchase #3	$11.70	10.522%	$12.9311	$12.93	$12.95	$12.90
Purchase #4	$128.34	6.848%	$137.1287	$137.13	$137.15	$137.10
Purchase #5	$84.67	9.734%	$92.9118	$92.91	$92.90	$92.90
Purchase #6	$151.56	3.290%	$156.5463	$156.55	$156.55	$156.50
Purchase #7	$130.39	13.501%	$147.994	$147.99	$148.00	$148.00
7 purchase totals =	$732.89		$796.2516	$796.25	$796.30	$796.10