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	$246.57	13.181%	$279.0704	$279.07	$279.05	$279.10
Purchase #2	$172.59	10.306%	$190.3771	$190.38	$190.40	$190.40
Purchase #3	$40.51	13.692%	$46.0566	$46.06	$46.05	$46.10
Purchase #4	$104.74	5.823%	$110.839	$110.84	$110.85	$110.80
Purchase #5	$47.25	11.735%	$52.7948	$52.79	$52.80	$52.80
Purchase #6	$190.73	8.851%	$207.6115	$207.61	$207.60	$207.60
Purchase #7	$118.41	10.285%	$130.5885	$130.59	$130.60	$130.60
7 purchase totals =	$920.80		$1,017.3379	$1,017.34	$1,017.35	$1,017.40