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	$24.55	13.526%	$27.8706	$27.87	$27.85	$27.90
Purchase #2	$190.91	7.194%	$204.6441	$204.64	$204.65	$204.60
Purchase #3	$95.50	3.803%	$99.1319	$99.13	$99.15	$99.10
Purchase #4	$57.80	3.112%	$59.5987	$59.60	$59.60	$59.60
Purchase #5	$113.54	3.294%	$117.28	$117.28	$117.30	$117.30
Purchase #6	$103.52	13.666%	$117.667	$117.67	$117.65	$117.70
Purchase #7	$185.30	4.568%	$193.7645	$193.76	$193.75	$193.80
7 purchase totals =	$771.12		$819.9568	$819.95	$819.95	$820.00