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	$161.78	6.723%	$172.6565	$172.66	$172.65	$172.70
Purchase #2	$242.49	11.858%	$271.2445	$271.24	$271.25	$271.20
Purchase #3	$171.33	8.293%	$185.5384	$185.54	$185.55	$185.50
Purchase #4	$96.44	3.372%	$99.692	$99.69	$99.70	$99.70
Purchase #5	$19.69	3.807%	$20.4396	$20.44	$20.45	$20.40
Purchase #6	$150.39	10.768%	$166.584	$166.58	$166.60	$166.60
Purchase #7	$94.38	10.476%	$104.2672	$104.27	$104.25	$104.30
7 purchase totals =	$936.50		$1,020.4222	$1,020.42	$1,020.45	$1,020.40