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	$150.95	10.326%	$166.5371	$166.54	$166.55	$166.50
Purchase #2	$163.43	5.408%	$172.2683	$172.27	$172.25	$172.30
Purchase #3	$57.79	12.526%	$65.0288	$65.03	$65.05	$65.00
Purchase #4	$128.86	4.193%	$134.2631	$134.26	$134.25	$134.30
Purchase #5	$92.94	13.459%	$105.4488	$105.45	$105.45	$105.40
Purchase #6	$195.31	13.529%	$221.7335	$221.73	$221.75	$221.70
Purchase #7	$11.37	6.527%	$12.1121	$12.11	$12.10	$12.10
7 purchase totals =	$800.65		$877.3917	$877.39	$877.40	$877.30