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	$79.74	13.439%	$90.4563	$90.46	$90.45	$90.50
Purchase #2	$50.85	13.435%	$57.6817	$57.68	$57.70	$57.70
Purchase #3	$236.45	8.139%	$255.6947	$255.69	$255.70	$255.70
Purchase #4	$227.46	5.563%	$240.1136	$240.11	$240.10	$240.10
Purchase #5	$20.86	5.141%	$21.9324	$21.93	$21.95	$21.90
Purchase #6	$58.32	10.745%	$64.5865	$64.59	$64.60	$64.60
Purchase #7	$81.61	11.749%	$91.1984	$91.20	$91.20	$91.20
7 purchase totals =	$755.29		$821.6636	$821.66	$821.70	$821.70