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	$155.53	7.159%	$166.6644	$166.66	$166.65	$166.70
Purchase #2	$136.34	7.474%	$146.5301	$146.53	$146.55	$146.50
Purchase #3	$85.56	11.174%	$95.1205	$95.12	$95.10	$95.10
Purchase #4	$16.27	10.153%	$17.9219	$17.92	$17.90	$17.90
Purchase #5	$82.63	8.714%	$89.8304	$89.83	$89.85	$89.80
Purchase #6	$185.75	7.747%	$200.1401	$200.14	$200.15	$200.10
Purchase #7	$137.75	5.349%	$145.1182	$145.12	$145.10	$145.10
7 purchase totals =	$799.83		$861.3256	$861.32	$861.30	$861.20