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	$40.63	4.301%	$42.3775	$42.38	$42.40	$42.40
Purchase #2	$77.51	12.857%	$87.4755	$87.48	$87.50	$87.50
Purchase #3	$53.49	11.719%	$59.7585	$59.76	$59.75	$59.80
Purchase #4	$157.98	4.689%	$165.3877	$165.39	$165.40	$165.40
Purchase #5	$75.70	9.868%	$83.1701	$83.17	$83.15	$83.20
Purchase #6	$29.91	7.213%	$32.0674	$32.07	$32.05	$32.10
Purchase #7	$147.25	11.455%	$164.1175	$164.12	$164.10	$164.10
7 purchase totals =	$582.47		$634.3542	$634.37	$634.35	$634.50