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	$83.65	5.542%	$88.2859	$88.29	$88.30	$88.30
Purchase #2	$37.72	11.631%	$42.1072	$42.11	$42.10	$42.10
Purchase #3	$109.49	7.831%	$118.0642	$118.06	$118.05	$118.10
Purchase #4	$49.48	11.815%	$55.3261	$55.33	$55.35	$55.30
Purchase #5	$59.82	3.750%	$62.0633	$62.06	$62.05	$62.10
Purchase #6	$97.47	10.652%	$107.8525	$107.85	$107.85	$107.90
Purchase #7	$154.71	6.257%	$164.3902	$164.39	$164.40	$164.40
7 purchase totals =	$592.34		$638.0894	$638.09	$638.10	$638.20