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	$33.54	3.737%	$34.7934	$34.79	$34.80	$34.80
Purchase #2	$235.65	12.699%	$265.5752	$265.58	$265.60	$265.60
Purchase #3	$250.49	10.777%	$277.4853	$277.49	$277.50	$277.50
Purchase #4	$132.71	10.703%	$146.914	$146.91	$146.90	$146.90
Purchase #5	$26.71	6.420%	$28.4248	$28.42	$28.40	$28.40
Purchase #6	$153.39	8.860%	$166.9804	$166.98	$167.00	$167.00
Purchase #7	$78.43	6.700%	$83.6848	$83.68	$83.70	$83.70
7 purchase totals =	$910.92		$1,003.8579	$1,003.85	$1,003.90	$1,003.90