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	$69.73	12.813%	$78.6645	$78.66	$78.65	$78.70
Purchase #2	$86.98	7.613%	$93.6018	$93.60	$93.60	$93.60
Purchase #3	$70.93	5.613%	$74.9113	$74.91	$74.90	$74.90
Purchase #4	$25.87	6.120%	$27.4532	$27.45	$27.45	$27.50
Purchase #5	$65.59	13.298%	$74.3122	$74.31	$74.30	$74.30
Purchase #6	$165.85	3.801%	$172.154	$172.15	$172.15	$172.20
Purchase #7	$139.30	3.511%	$144.1908	$144.19	$144.20	$144.20
7 purchase totals =	$624.25		$665.2878	$665.27	$665.25	$665.40