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	$27.71	6.497%	$29.5103	$29.51	$29.50	$29.50
Purchase #2	$77.66	6.429%	$82.6528	$82.65	$82.65	$82.70
Purchase #3	$218.40	3.748%	$226.5856	$226.59	$226.60	$226.60
Purchase #4	$67.49	10.477%	$74.5609	$74.56	$74.55	$74.60
Purchase #5	$114.33	3.325%	$118.1315	$118.13	$118.15	$118.10
Purchase #6	$111.39	10.722%	$123.3332	$123.33	$123.35	$123.30
Purchase #7	$131.60	4.188%	$137.1114	$137.11	$137.10	$137.10
7 purchase totals =	$748.58		$791.8857	$791.88	$791.90	$791.90