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	$246.42	4.196%	$256.7598	$256.76	$256.75	$256.80
Purchase #2	$172.62	8.127%	$186.6488	$186.65	$186.65	$186.60
Purchase #3	$123.30	3.308%	$127.3788	$127.38	$127.40	$127.40
Purchase #4	$227.60	3.698%	$236.0166	$236.02	$236.00	$236.00
Purchase #5	$22.60	8.155%	$24.443	$24.44	$24.45	$24.40
Purchase #6	$198.42	10.491%	$219.2362	$219.24	$219.25	$219.20
Purchase #7	$37.65	8.604%	$40.8894	$40.89	$40.90	$40.90
7 purchase totals =	$1,028.61		$1,091.3726	$1,091.38	$1,091.40	$1,091.30