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	$19.30	13.148%	$21.8376	$21.84	$21.85	$21.80
Purchase #2	$120.81	4.804%	$126.6137	$126.61	$126.60	$126.60
Purchase #3	$209.48	4.591%	$219.0972	$219.10	$219.10	$219.10
Purchase #4	$81.97	4.795%	$85.9005	$85.90	$85.90	$85.90
Purchase #5	$155.68	10.567%	$172.1307	$172.13	$172.15	$172.10
Purchase #6	$77.49	6.817%	$82.7725	$82.77	$82.75	$82.80
Purchase #7	$85.62	7.685%	$92.1999	$92.20	$92.20	$92.20
7 purchase totals =	$750.35		$800.5521	$800.55	$800.55	$800.50