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	$40.28	11.782%	$45.0258	$45.03	$45.05	$45.00
Purchase #2	$151.90	9.484%	$166.3062	$166.31	$166.30	$166.30
Purchase #3	$179.61	3.842%	$186.5106	$186.51	$186.50	$186.50
Purchase #4	$121.83	8.484%	$132.1661	$132.17	$132.15	$132.20
Purchase #5	$216.66	7.745%	$233.4403	$233.44	$233.45	$233.40
Purchase #6	$37.69	6.174%	$40.017	$40.02	$40.00	$40.00
Purchase #7	$57.97	10.697%	$64.1711	$64.17	$64.15	$64.20
7 purchase totals =	$805.94		$867.6371	$867.65	$867.60	$867.60