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	$244.53	4.491%	$255.5118	$255.51	$255.50	$255.50
Purchase #2	$58.53	10.639%	$64.757	$64.76	$64.75	$64.80
Purchase #3	$131.90	5.305%	$138.8973	$138.90	$138.90	$138.90
Purchase #4	$33.93	12.685%	$38.234	$38.23	$38.25	$38.20
Purchase #5	$212.35	6.132%	$225.3713	$225.37	$225.35	$225.40
Purchase #6	$11.87	8.591%	$12.8898	$12.89	$12.90	$12.90
Purchase #7	$201.68	10.489%	$222.8342	$222.83	$222.85	$222.80
7 purchase totals =	$894.79		$958.4954	$958.49	$958.50	$958.50