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	$189.52	11.640%	$211.5801	$211.58	$211.60	$211.60
Purchase #2	$96.72	9.510%	$105.9181	$105.92	$105.90	$105.90
Purchase #3	$61.25	12.728%	$69.0459	$69.05	$69.05	$69.00
Purchase #4	$61.58	6.373%	$65.5045	$65.50	$65.50	$65.50
Purchase #5	$108.87	9.121%	$118.8	$118.80	$118.80	$118.80
Purchase #6	$26.27	7.849%	$28.3319	$28.33	$28.35	$28.30
Purchase #7	$100.26	3.631%	$103.9004	$103.90	$103.90	$103.90
7 purchase totals =	$644.47		$703.0809	$703.08	$703.10	$703.00