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	$74.43	4.332%	$77.6543	$77.65	$77.65	$77.70
Purchase #2	$39.75	9.371%	$43.475	$43.48	$43.50	$43.50
Purchase #3	$116.92	13.362%	$132.5429	$132.54	$132.55	$132.50
Purchase #4	$98.26	3.411%	$101.6116	$101.61	$101.60	$101.60
Purchase #5	$17.94	11.743%	$20.0467	$20.05	$20.05	$20.00
Purchase #6	$31.72	5.738%	$33.5401	$33.54	$33.55	$33.50
Purchase #7	$13.54	4.779%	$14.1871	$14.19	$14.20	$14.20
7 purchase totals =	$392.56		$423.0577	$423.06	$423.10	$423.00