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	$55.55	4.206%	$57.8864	$57.89	$57.90	$57.90
Purchase #2	$102.77	6.228%	$109.1705	$109.17	$109.15	$109.20
Purchase #3	$107.34	3.107%	$110.6751	$110.68	$110.70	$110.70
Purchase #4	$44.40	12.680%	$50.0299	$50.03	$50.05	$50.00
Purchase #5	$56.49	5.359%	$59.5173	$59.52	$59.50	$59.50
Purchase #6	$92.26	7.237%	$98.9369	$98.94	$98.95	$98.90
Purchase #7	$100.54	5.256%	$105.8244	$105.82	$105.80	$105.80
7 purchase totals =	$559.35		$592.0405	$592.05	$592.05	$592.00