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	$59.71	10.764%	$66.1372	$66.14	$66.15	$66.10
Purchase #2	$178.42	6.557%	$190.119	$190.12	$190.10	$190.10
Purchase #3	$34.57	10.137%	$38.0744	$38.07	$38.05	$38.10
Purchase #4	$147.33	6.286%	$156.5912	$156.59	$156.60	$156.60
Purchase #5	$51.91	9.205%	$56.6883	$56.69	$56.70	$56.70
Purchase #6	$141.50	6.258%	$150.3551	$150.36	$150.35	$150.40
Purchase #7	$95.31	13.298%	$107.9843	$107.98	$108.00	$108.00
7 purchase totals =	$708.75		$765.9495	$765.95	$765.95	$766.00