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	$152.86	12.757%	$172.3604	$172.36	$172.35	$172.40
Purchase #2	$114.65	8.602%	$124.5122	$124.51	$124.50	$124.50
Purchase #3	$134.75	12.654%	$151.8013	$151.80	$151.80	$151.80
Purchase #4	$97.57	8.379%	$105.7454	$105.75	$105.75	$105.70
Purchase #5	$158.89	6.279%	$168.8667	$168.87	$168.85	$168.90
Purchase #6	$67.61	4.357%	$70.5558	$70.56	$70.55	$70.60
Purchase #7	$54.49	6.404%	$57.9795	$57.98	$58.00	$58.00
7 purchase totals =	$780.82		$851.8213	$851.83	$851.80	$851.90