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	$100.68	12.797%	$113.564	$113.56	$113.55	$113.60
Purchase #2	$98.83	4.424%	$103.2022	$103.20	$103.20	$103.20
Purchase #3	$151.81	13.737%	$172.6641	$172.66	$172.65	$172.70
Purchase #4	$238.28	9.521%	$260.9666	$260.97	$260.95	$261.00
Purchase #5	$157.97	8.661%	$171.6518	$171.65	$171.65	$171.70
Purchase #6	$56.26	5.713%	$59.4741	$59.47	$59.45	$59.50
Purchase #7	$52.86	8.139%	$57.1623	$57.16	$57.15	$57.20
7 purchase totals =	$856.69		$938.6851	$938.67	$938.60	$938.90