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	$34.41	13.267%	$38.9752	$38.98	$39.00	$39.00
Purchase #2	$249.56	6.186%	$264.9978	$265.00	$265.00	$265.00
Purchase #3	$116.31	4.180%	$121.1718	$121.17	$121.15	$121.20
Purchase #4	$154.89	13.555%	$175.8853	$175.89	$175.90	$175.90
Purchase #5	$214.74	10.861%	$238.0629	$238.06	$238.05	$238.10
Purchase #6	$146.94	10.780%	$162.7801	$162.78	$162.80	$162.80
Purchase #7	$91.77	7.570%	$98.717	$98.72	$98.70	$98.70
7 purchase totals =	$1,008.62		$1,100.5901	$1,100.60	$1,100.60	$1,100.70