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	$36.59	12.358%	$41.1118	$41.11	$41.10	$41.10
Purchase #2	$226.67	6.623%	$241.6824	$241.68	$241.70	$241.70
Purchase #3	$108.71	13.264%	$123.1293	$123.13	$123.15	$123.10
Purchase #4	$36.39	3.253%	$37.5738	$37.57	$37.55	$37.60
Purchase #5	$52.77	10.837%	$58.4887	$58.49	$58.50	$58.50
Purchase #6	$91.64	4.404%	$95.6758	$95.68	$95.70	$95.70
Purchase #7	$35.96	5.224%	$37.8386	$37.84	$37.85	$37.80
7 purchase totals =	$588.73		$635.5004	$635.50	$635.55	$635.50