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	$26.66	7.241%	$28.5905	$28.59	$28.60	$28.60
Purchase #2	$154.73	13.324%	$175.3462	$175.35	$175.35	$175.30
Purchase #3	$133.81	5.466%	$141.1241	$141.12	$141.10	$141.10
Purchase #4	$111.41	3.722%	$115.5567	$115.56	$115.55	$115.60
Purchase #5	$46.69	13.800%	$53.1332	$53.13	$53.15	$53.10
Purchase #6	$52.38	13.461%	$59.4309	$59.43	$59.45	$59.40
Purchase #7	$217.93	8.809%	$237.1275	$237.13	$237.15	$237.10
7 purchase totals =	$743.61		$810.3091	$810.31	$810.35	$810.20