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	$147.32	12.678%	$165.9972	$166.00	$166.00	$166.00
Purchase #2	$227.62	13.136%	$257.5202	$257.52	$257.50	$257.50
Purchase #3	$127.51	13.605%	$144.8577	$144.86	$144.85	$144.90
Purchase #4	$57.56	8.780%	$62.6138	$62.61	$62.60	$62.60
Purchase #5	$72.53	11.462%	$80.8434	$80.84	$80.85	$80.80
Purchase #6	$182.98	8.581%	$198.6815	$198.68	$198.70	$198.70
Purchase #7	$44.98	12.142%	$50.4415	$50.44	$50.45	$50.40
7 purchase totals =	$860.50		$960.9553	$960.95	$960.95	$960.90