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	$116.83	3.173%	$120.537	$120.54	$120.55	$120.50
Purchase #2	$103.77	4.684%	$108.6306	$108.63	$108.65	$108.60
Purchase #3	$47.32	12.719%	$53.3386	$53.34	$53.35	$53.30
Purchase #4	$194.74	12.497%	$219.0767	$219.08	$219.10	$219.10
Purchase #5	$145.28	10.706%	$160.8337	$160.83	$160.85	$160.80
Purchase #6	$80.27	11.464%	$89.4722	$89.47	$89.45	$89.50
Purchase #7	$58.51	6.605%	$62.3746	$62.37	$62.35	$62.40
7 purchase totals =	$746.72		$814.2634	$814.26	$814.30	$814.20