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	$140.32	8.448%	$152.1742	$152.17	$152.15	$152.20
Purchase #2	$228.76	13.336%	$259.2674	$259.27	$259.25	$259.30
Purchase #3	$121.68	6.862%	$130.0297	$130.03	$130.05	$130.00
Purchase #4	$28.49	4.443%	$29.7558	$29.76	$29.75	$29.80
Purchase #5	$31.38	7.792%	$33.8251	$33.83	$33.85	$33.80
Purchase #6	$41.56	8.376%	$45.0411	$45.04	$45.05	$45.00
Purchase #7	$56.56	8.768%	$61.5192	$61.52	$61.50	$61.50
7 purchase totals =	$648.75		$711.6125	$711.62	$711.60	$711.60