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	$100.96	3.331%	$104.323	$104.32	$104.30	$104.30
Purchase #2	$91.92	11.412%	$102.4099	$102.41	$102.40	$102.40
Purchase #3	$28.97	3.218%	$29.9023	$29.90	$29.90	$29.90
Purchase #4	$133.39	9.486%	$146.0434	$146.04	$146.05	$146.00
Purchase #5	$76.74	10.801%	$85.0287	$85.03	$85.05	$85.00
Purchase #6	$50.25	11.711%	$56.1348	$56.13	$56.15	$56.10
Purchase #7	$50.29	7.816%	$54.2207	$54.22	$54.20	$54.20
7 purchase totals =	$532.52		$578.0628	$578.05	$578.05	$577.90