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	$124.89	9.219%	$136.4036	$136.40	$136.40	$136.40
Purchase #2	$97.77	11.371%	$108.8874	$108.89	$108.90	$108.90
Purchase #3	$41.57	13.766%	$47.2925	$47.29	$47.30	$47.30
Purchase #4	$112.56	13.377%	$127.6172	$127.62	$127.60	$127.60
Purchase #5	$53.78	6.748%	$57.4091	$57.41	$57.40	$57.40
Purchase #6	$121.32	9.761%	$133.162	$133.16	$133.15	$133.20
Purchase #7	$49.88	6.244%	$52.9945	$52.99	$53.00	$53.00
7 purchase totals =	$601.77		$663.7663	$663.76	$663.75	$663.80