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	$128.60	8.195%	$139.1388	$139.14	$139.15	$139.10
Purchase #2	$51.86	9.654%	$56.8666	$56.87	$56.85	$56.90
Purchase #3	$57.86	13.156%	$65.4721	$65.47	$65.45	$65.50
Purchase #4	$82.51	10.400%	$91.091	$91.09	$91.10	$91.10
Purchase #5	$238.41	6.802%	$254.6266	$254.63	$254.65	$254.60
Purchase #6	$27.45	5.635%	$28.9968	$29.00	$29.00	$29.00
Purchase #7	$127.74	4.675%	$133.7118	$133.71	$133.70	$133.70
7 purchase totals =	$714.43		$769.9037	$769.91	$769.90	$769.90