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	$52.59	6.546%	$56.0325	$56.03	$56.05	$56.00
Purchase #2	$151.56	6.442%	$161.3235	$161.32	$161.30	$161.30
Purchase #3	$96.58	4.183%	$100.6199	$100.62	$100.60	$100.60
Purchase #4	$161.28	12.326%	$181.1594	$181.16	$181.15	$181.20
Purchase #5	$14.98	13.662%	$17.0266	$17.03	$17.05	$17.00
Purchase #6	$199.81	5.642%	$211.0833	$211.08	$211.10	$211.10
Purchase #7	$86.52	4.424%	$90.3476	$90.35	$90.35	$90.30
7 purchase totals =	$763.32		$817.5928	$817.59	$817.60	$817.50