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	$129.34	7.728%	$139.3354	$139.34	$139.35	$139.30
Purchase #2	$234.54	8.797%	$255.1725	$255.17	$255.15	$255.20
Purchase #3	$194.55	5.309%	$204.8787	$204.88	$204.90	$204.90
Purchase #4	$75.69	8.635%	$82.2258	$82.23	$82.25	$82.20
Purchase #5	$157.37	13.504%	$178.6212	$178.62	$178.60	$178.60
Purchase #6	$29.75	9.869%	$32.686	$32.69	$32.70	$32.70
Purchase #7	$135.42	11.632%	$151.1721	$151.17	$151.15	$151.20
7 purchase totals =	$956.66		$1,044.0917	$1,044.10	$1,044.10	$1,044.10