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	$80.90	10.744%	$89.5919	$89.59	$89.60	$89.60
Purchase #2	$154.63	11.461%	$172.3521	$172.35	$172.35	$172.40
Purchase #3	$209.51	10.813%	$232.1643	$232.16	$232.15	$232.20
Purchase #4	$188.98	8.765%	$205.5441	$205.54	$205.55	$205.50
Purchase #5	$247.31	10.327%	$272.8497	$272.85	$272.85	$272.80
Purchase #6	$132.70	6.144%	$140.8531	$140.85	$140.85	$140.90
Purchase #7	$166.37	12.643%	$187.4042	$187.40	$187.40	$187.40
7 purchase totals =	$1,180.40		$1,300.7594	$1,300.74	$1,300.75	$1,300.80