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	$134.52	12.386%	$151.1816	$151.18	$151.20	$151.20
Purchase #2	$210.86	6.269%	$224.0788	$224.08	$224.10	$224.10
Purchase #3	$135.39	11.472%	$150.9219	$150.92	$150.90	$150.90
Purchase #4	$107.57	5.408%	$113.3874	$113.39	$113.40	$113.40
Purchase #5	$166.34	12.106%	$186.4771	$186.48	$186.50	$186.50
Purchase #6	$24.52	4.339%	$25.5839	$25.58	$25.60	$25.60
Purchase #7	$83.62	8.442%	$90.6792	$90.68	$90.70	$90.70
7 purchase totals =	$862.82		$942.3099	$942.31	$942.40	$942.40