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	$236.94	5.341%	$249.595	$249.60	$249.60	$249.60
Purchase #2	$204.59	3.142%	$211.0182	$211.02	$211.00	$211.00
Purchase #3	$10.42	10.648%	$11.5295	$11.53	$11.55	$11.50
Purchase #4	$35.67	10.424%	$39.3882	$39.39	$39.40	$39.40
Purchase #5	$121.69	4.657%	$127.3571	$127.36	$127.35	$127.40
Purchase #6	$120.48	9.461%	$131.8786	$131.88	$131.90	$131.90
Purchase #7	$114.98	13.428%	$130.4195	$130.42	$130.40	$130.40
7 purchase totals =	$844.77		$901.1861	$901.20	$901.20	$901.20