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	$165.40	7.826%	$178.3442	$178.34	$178.35	$178.30
Purchase #2	$153.96	11.660%	$171.9117	$171.91	$171.90	$171.90
Purchase #3	$116.35	9.580%	$127.4963	$127.50	$127.50	$127.50
Purchase #4	$65.60	6.376%	$69.7827	$69.78	$69.80	$69.80
Purchase #5	$128.51	4.850%	$134.7427	$134.74	$134.75	$134.70
Purchase #6	$99.72	4.438%	$104.1456	$104.15	$104.15	$104.10
Purchase #7	$60.77	5.436%	$64.0735	$64.07	$64.05	$64.10
7 purchase totals =	$790.31		$850.4967	$850.49	$850.50	$850.40