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	$6.49	12.189%	$7.2811	$7.28	$7.30	$7.30
Purchase #2	$188.32	6.555%	$200.6644	$200.66	$200.65	$200.70
Purchase #3	$202.33	4.287%	$211.0039	$211.00	$211.00	$211.00
Purchase #4	$49.60	9.266%	$54.1959	$54.20	$54.20	$54.20
Purchase #5	$104.75	13.146%	$118.5204	$118.52	$118.50	$118.50
Purchase #6	$178.72	9.821%	$196.2721	$196.27	$196.25	$196.30
Purchase #7	$99.33	4.278%	$103.5793	$103.58	$103.60	$103.60
7 purchase totals =	$829.54		$891.5171	$891.51	$891.50	$891.60