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	$6.87	13.212%	$7.7777	$7.78	$7.80	$7.80
Purchase #2	$101.65	4.849%	$106.579	$106.58	$106.60	$106.60
Purchase #3	$75.60	9.257%	$82.5983	$82.60	$82.60	$82.60
Purchase #4	$127.44	12.282%	$143.0922	$143.09	$143.10	$143.10
Purchase #5	$120.94	13.534%	$137.308	$137.31	$137.30	$137.30
Purchase #6	$27.32	3.612%	$28.3068	$28.31	$28.30	$28.30
Purchase #7	$56.47	13.596%	$64.1477	$64.15	$64.15	$64.10
7 purchase totals =	$516.29		$569.8097	$569.82	$569.85	$569.80