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	$236.88	7.380%	$254.3617	$254.36	$254.35	$254.40
Purchase #2	$21.42	10.291%	$23.6243	$23.62	$23.60	$23.60
Purchase #3	$119.82	6.760%	$127.9198	$127.92	$127.90	$127.90
Purchase #4	$67.27	5.193%	$70.7633	$70.76	$70.75	$70.80
Purchase #5	$85.42	13.839%	$97.2413	$97.24	$97.25	$97.20
Purchase #6	$34.60	3.571%	$35.8356	$35.84	$35.85	$35.80
Purchase #7	$52.81	6.655%	$56.3245	$56.32	$56.30	$56.30
7 purchase totals =	$618.22		$666.0705	$666.06	$666.00	$666.00