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	$73.76	5.776%	$78.0204	$78.02	$78.00	$78.00
Purchase #2	$40.69	6.838%	$43.4724	$43.47	$43.45	$43.50
Purchase #3	$237.44	9.150%	$259.1658	$259.17	$259.15	$259.20
Purchase #4	$105.83	13.712%	$120.3414	$120.34	$120.35	$120.30
Purchase #5	$48.34	10.651%	$53.4887	$53.49	$53.50	$53.50
Purchase #6	$22.70	7.178%	$24.3294	$24.33	$24.35	$24.30
Purchase #7	$141.62	6.802%	$151.253	$151.25	$151.25	$151.30
7 purchase totals =	$670.38		$730.0711	$730.07	$730.05	$730.10