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	$227.28	10.815%	$251.8603	$251.86	$251.85	$251.90
Purchase #2	$103.70	7.426%	$111.4008	$111.40	$111.40	$111.40
Purchase #3	$15.95	8.654%	$17.3303	$17.33	$17.35	$17.30
Purchase #4	$223.92	6.346%	$238.13	$238.13	$238.15	$238.10
Purchase #5	$36.49	10.445%	$40.3014	$40.30	$40.30	$40.30
Purchase #6	$68.54	4.402%	$71.5571	$71.56	$71.55	$71.60
Purchase #7	$222.82	10.634%	$246.5147	$246.51	$246.50	$246.50
7 purchase totals =	$898.70		$977.0946	$977.09	$977.10	$977.10