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	$77.70	11.284%	$86.4677	$86.47	$86.45	$86.50
Purchase #2	$137.44	10.631%	$152.0512	$152.05	$152.05	$152.10
Purchase #3	$84.64	7.704%	$91.1607	$91.16	$91.15	$91.20
Purchase #4	$126.97	11.323%	$141.3468	$141.35	$141.35	$141.30
Purchase #5	$122.42	3.159%	$126.2872	$126.29	$126.30	$126.30
Purchase #6	$142.85	5.109%	$150.1482	$150.15	$150.15	$150.10
Purchase #7	$129.70	10.113%	$142.8166	$142.82	$142.80	$142.80
7 purchase totals =	$821.72		$890.2784	$890.29	$890.25	$890.30