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	$117.33	4.851%	$123.0217	$123.02	$123.00	$123.00
Purchase #2	$11.29	10.724%	$12.5007	$12.50	$12.50	$12.50
Purchase #3	$96.43	13.256%	$109.2128	$109.21	$109.20	$109.20
Purchase #4	$40.75	9.604%	$44.6636	$44.66	$44.65	$44.70
Purchase #5	$9.34	9.145%	$10.1941	$10.19	$10.20	$10.20
Purchase #6	$54.34	10.210%	$59.8881	$59.89	$59.90	$59.90
Purchase #7	$149.72	13.585%	$170.0595	$170.06	$170.05	$170.10
7 purchase totals =	$479.20		$529.5405	$529.53	$529.50	$529.60