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	$227.53	4.567%	$237.9213	$237.92	$237.90	$237.90
Purchase #2	$185.48	10.747%	$205.4135	$205.41	$205.40	$205.40
Purchase #3	$94.34	5.583%	$99.607	$99.61	$99.60	$99.60
Purchase #4	$182.62	4.739%	$191.2744	$191.27	$191.25	$191.30
Purchase #5	$112.92	7.584%	$121.4839	$121.48	$121.50	$121.50
Purchase #6	$72.96	7.707%	$78.583	$78.58	$78.60	$78.60
Purchase #7	$54.42	4.158%	$56.6828	$56.68	$56.70	$56.70
7 purchase totals =	$930.27		$990.9659	$990.95	$990.95	$991.00