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	$143.53	11.695%	$160.3158	$160.32	$160.30	$160.30
Purchase #2	$53.45	9.567%	$58.5636	$58.56	$58.55	$58.60
Purchase #3	$37.71	12.133%	$42.2854	$42.29	$42.30	$42.30
Purchase #4	$170.75	13.838%	$194.3784	$194.38	$194.40	$194.40
Purchase #5	$11.52	13.341%	$13.0569	$13.06	$13.05	$13.10
Purchase #6	$91.28	9.345%	$99.8101	$99.81	$99.80	$99.80
Purchase #7	$108.96	3.497%	$112.7703	$112.77	$112.75	$112.80
7 purchase totals =	$617.20		$681.1805	$681.19	$681.15	$681.30