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	$81.31	12.435%	$91.4209	$91.42	$91.40	$91.40
Purchase #2	$83.50	8.188%	$90.337	$90.34	$90.35	$90.30
Purchase #3	$148.87	13.250%	$168.5953	$168.60	$168.60	$168.60
Purchase #4	$114.31	11.218%	$127.1333	$127.13	$127.15	$127.10
Purchase #5	$139.92	13.327%	$158.5671	$158.57	$158.55	$158.60
Purchase #6	$126.72	5.658%	$133.8898	$133.89	$133.90	$133.90
Purchase #7	$114.62	11.836%	$128.1864	$128.19	$128.20	$128.20
7 purchase totals =	$809.25		$898.1298	$898.14	$898.15	$898.10