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	$237.85	4.816%	$249.3049	$249.30	$249.30	$249.30
Purchase #2	$138.50	12.104%	$155.264	$155.26	$155.25	$155.30
Purchase #3	$152.77	3.723%	$158.4576	$158.46	$158.45	$158.50
Purchase #4	$47.51	3.763%	$49.2978	$49.30	$49.30	$49.30
Purchase #5	$50.66	5.296%	$53.343	$53.34	$53.35	$53.30
Purchase #6	$99.43	5.577%	$104.9752	$104.98	$105.00	$105.00
Purchase #7	$128.32	12.384%	$144.2111	$144.21	$144.20	$144.20
7 purchase totals =	$855.04		$914.8536	$914.85	$914.85	$914.90