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	$76.28	3.421%	$78.8895	$78.89	$78.90	$78.90
Purchase #2	$114.62	7.830%	$123.5947	$123.59	$123.60	$123.60
Purchase #3	$176.42	9.297%	$192.8218	$192.82	$192.80	$192.80
Purchase #4	$126.35	3.722%	$131.0527	$131.05	$131.05	$131.10
Purchase #5	$232.97	8.129%	$251.9081	$251.91	$251.90	$251.90
Purchase #6	$49.89	8.413%	$54.0872	$54.09	$54.10	$54.10
Purchase #7	$235.65	7.315%	$252.8878	$252.89	$252.90	$252.90
7 purchase totals =	$1,012.18		$1,085.2418	$1,085.24	$1,085.25	$1,085.30