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	$65.42	8.388%	$70.9074	$70.91	$70.90	$70.90
Purchase #2	$80.32	7.560%	$86.3922	$86.39	$86.40	$86.40
Purchase #3	$158.29	5.269%	$166.6303	$166.63	$166.65	$166.60
Purchase #4	$199.86	5.487%	$210.8263	$210.83	$210.85	$210.80
Purchase #5	$12.92	5.150%	$13.5854	$13.59	$13.60	$13.60
Purchase #6	$79.87	13.613%	$90.7427	$90.74	$90.75	$90.70
Purchase #7	$51.62	4.516%	$53.9512	$53.95	$53.95	$54.00
7 purchase totals =	$648.30		$693.0355	$693.04	$693.10	$693.00