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	$142.43	11.304%	$158.5303	$158.53	$158.55	$158.50
Purchase #2	$96.47	13.635%	$109.6237	$109.62	$109.60	$109.60
Purchase #3	$86.41	4.487%	$90.2872	$90.29	$90.30	$90.30
Purchase #4	$52.32	4.253%	$54.5452	$54.55	$54.55	$54.50
Purchase #5	$65.51	13.541%	$74.3807	$74.38	$74.40	$74.40
Purchase #6	$232.88	8.341%	$252.3045	$252.30	$252.30	$252.30
Purchase #7	$168.49	8.416%	$182.6701	$182.67	$182.65	$182.70
7 purchase totals =	$844.51		$922.3417	$922.34	$922.35	$922.30