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	$215.25	11.801%	$240.6517	$240.65	$240.65	$240.70
Purchase #2	$57.98	3.377%	$59.938	$59.94	$59.95	$59.90
Purchase #3	$79.39	7.255%	$85.1497	$85.15	$85.15	$85.10
Purchase #4	$123.27	3.535%	$127.6276	$127.63	$127.65	$127.60
Purchase #5	$57.72	3.122%	$59.522	$59.52	$59.50	$59.50
Purchase #6	$54.81	9.180%	$59.8416	$59.84	$59.85	$59.80
Purchase #7	$42.59	12.495%	$47.9116	$47.91	$47.90	$47.90
7 purchase totals =	$631.01		$680.6422	$680.64	$680.65	$680.50