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	$99.99	3.466%	$103.4557	$103.46	$103.45	$103.50
Purchase #2	$242.34	5.539%	$255.7632	$255.76	$255.75	$255.80
Purchase #3	$14.95	13.479%	$16.9651	$16.97	$16.95	$17.00
Purchase #4	$82.59	3.213%	$85.2436	$85.24	$85.25	$85.20
Purchase #5	$95.44	4.118%	$99.3702	$99.37	$99.35	$99.40
Purchase #6	$48.52	12.343%	$54.5088	$54.51	$54.50	$54.50
Purchase #7	$165.54	5.188%	$174.1282	$174.13	$174.15	$174.10
7 purchase totals =	$749.37		$789.4348	$789.44	$789.40	$789.50