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	$223.90	13.157%	$253.3585	$253.36	$253.35	$253.40
Purchase #2	$102.99	10.229%	$113.5248	$113.52	$113.50	$113.50
Purchase #3	$127.76	12.835%	$144.158	$144.16	$144.15	$144.20
Purchase #4	$38.27	12.485%	$43.048	$43.05	$43.05	$43.00
Purchase #5	$232.39	13.442%	$263.6279	$263.63	$263.65	$263.60
Purchase #6	$79.52	12.103%	$89.1443	$89.14	$89.15	$89.10
Purchase #7	$26.98	6.592%	$28.7585	$28.76	$28.75	$28.80
7 purchase totals =	$831.81		$935.6200	$935.62	$935.60	$935.60