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	$240.30	6.772%	$256.5731	$256.57	$256.55	$256.60
Purchase #2	$71.72	10.392%	$79.1731	$79.17	$79.15	$79.20
Purchase #3	$237.60	4.176%	$247.5222	$247.52	$247.50	$247.50
Purchase #4	$62.43	9.168%	$68.1536	$68.15	$68.15	$68.20
Purchase #5	$28.82	11.372%	$32.0974	$32.10	$32.10	$32.10
Purchase #6	$95.73	4.601%	$100.1345	$100.13	$100.15	$100.10
Purchase #7	$152.75	3.810%	$158.5698	$158.57	$158.55	$158.60
7 purchase totals =	$889.35		$942.2237	$942.21	$942.15	$942.30