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	$79.27	13.415%	$89.9041	$89.90	$89.90	$89.90
Purchase #2	$61.76	5.655%	$65.2525	$65.25	$65.25	$65.30
Purchase #3	$76.39	6.680%	$81.4929	$81.49	$81.50	$81.50
Purchase #4	$66.96	11.568%	$74.7059	$74.71	$74.70	$74.70
Purchase #5	$156.54	10.406%	$172.8296	$172.83	$172.85	$172.80
Purchase #6	$120.65	10.524%	$133.3472	$133.35	$133.35	$133.30
Purchase #7	$6.83	12.233%	$7.6655	$7.67	$7.65	$7.70
7 purchase totals =	$568.40		$625.1977	$625.20	$625.20	$625.20