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	$57.39	3.104%	$59.1714	$59.17	$59.15	$59.20
Purchase #2	$39.56	6.604%	$42.1725	$42.17	$42.15	$42.20
Purchase #3	$119.78	3.582%	$124.0705	$124.07	$124.05	$124.10
Purchase #4	$107.58	4.588%	$112.5158	$112.52	$112.50	$112.50
Purchase #5	$6.51	7.261%	$6.9827	$6.98	$7.00	$7.00
Purchase #6	$67.99	5.845%	$71.964	$71.96	$71.95	$72.00
Purchase #7	$241.84	5.605%	$255.3951	$255.40	$255.40	$255.40
7 purchase totals =	$640.65		$672.2720	$672.27	$672.20	$672.40