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	$92.35	8.308%	$100.0224	$100.02	$100.00	$100.00
Purchase #2	$220.87	4.303%	$230.374	$230.37	$230.35	$230.40
Purchase #3	$78.36	4.706%	$82.0476	$82.05	$82.05	$82.00
Purchase #4	$166.27	13.462%	$188.6533	$188.65	$188.65	$188.70
Purchase #5	$173.96	12.563%	$195.8146	$195.81	$195.80	$195.80
Purchase #6	$39.59	7.575%	$42.5889	$42.59	$42.60	$42.60
Purchase #7	$214.51	5.844%	$227.046	$227.05	$227.05	$227.00
7 purchase totals =	$985.91		$1,066.5468	$1,066.54	$1,066.50	$1,066.50