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	$245.57	4.805%	$257.3696	$257.37	$257.35	$257.40
Purchase #2	$50.25	12.299%	$56.4302	$56.43	$56.45	$56.40
Purchase #3	$54.38	10.151%	$59.9001	$59.90	$59.90	$59.90
Purchase #4	$23.52	12.753%	$26.5195	$26.52	$26.50	$26.50
Purchase #5	$55.76	7.539%	$59.9637	$59.96	$59.95	$60.00
Purchase #6	$122.38	5.337%	$128.9114	$128.91	$128.90	$128.90
Purchase #7	$46.77	9.131%	$51.0406	$51.04	$51.05	$51.00
7 purchase totals =	$598.63		$640.1351	$640.13	$640.10	$640.10