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	$65.27	7.392%	$70.0948	$70.09	$70.10	$70.10
Purchase #2	$56.34	10.574%	$62.2974	$62.30	$62.30	$62.30
Purchase #3	$156.85	9.454%	$171.6786	$171.68	$171.70	$171.70
Purchase #4	$170.83	11.456%	$190.4003	$190.40	$190.40	$190.40
Purchase #5	$114.32	13.298%	$129.5223	$129.52	$129.50	$129.50
Purchase #6	$145.66	4.164%	$151.7253	$151.73	$151.75	$151.70
Purchase #7	$97.63	6.627%	$104.0999	$104.10	$104.10	$104.10
7 purchase totals =	$806.90		$879.8186	$879.82	$879.85	$879.80