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	$161.62	4.538%	$168.9543	$168.95	$168.95	$169.00
Purchase #2	$37.53	10.343%	$41.4117	$41.41	$41.40	$41.40
Purchase #3	$127.88	7.481%	$137.4467	$137.45	$137.45	$137.40
Purchase #4	$98.70	6.326%	$104.9438	$104.94	$104.95	$104.90
Purchase #5	$49.83	8.705%	$54.1677	$54.17	$54.15	$54.20
Purchase #6	$137.52	3.521%	$142.3621	$142.36	$142.35	$142.40
Purchase #7	$98.43	5.249%	$103.5966	$103.60	$103.60	$103.60
7 purchase totals =	$711.51		$752.8829	$752.88	$752.85	$752.90