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	$54.60	10.147%	$60.1403	$60.14	$60.15	$60.10
Purchase #2	$95.77	10.247%	$105.5836	$105.58	$105.60	$105.60
Purchase #3	$96.71	13.289%	$109.5618	$109.56	$109.55	$109.60
Purchase #4	$76.27	8.384%	$82.6645	$82.66	$82.65	$82.70
Purchase #5	$121.34	10.623%	$134.2299	$134.23	$134.25	$134.20
Purchase #6	$18.51	12.563%	$20.8354	$20.84	$20.85	$20.80
Purchase #7	$41.65	12.489%	$46.8517	$46.85	$46.85	$46.90
7 purchase totals =	$504.85		$559.8672	$559.86	$559.90	$559.90