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	$100.82	10.413%	$111.3184	$111.32	$111.30	$111.30
Purchase #2	$185.78	5.424%	$195.8567	$195.86	$195.85	$195.90
Purchase #3	$238.62	6.726%	$254.6696	$254.67	$254.65	$254.70
Purchase #4	$117.53	9.185%	$128.3251	$128.33	$128.35	$128.30
Purchase #5	$36.55	11.201%	$40.644	$40.64	$40.65	$40.60
Purchase #6	$55.97	4.708%	$58.6051	$58.61	$58.60	$58.60
Purchase #7	$51.50	13.444%	$58.4237	$58.42	$58.40	$58.40
7 purchase totals =	$786.77		$847.8426	$847.85	$847.80	$847.80