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	$158.95	13.562%	$180.5068	$180.51	$180.50	$180.50
Purchase #2	$169.27	11.144%	$188.1334	$188.13	$188.15	$188.10
Purchase #3	$82.55	8.529%	$89.5907	$89.59	$89.60	$89.60
Purchase #4	$79.59	11.179%	$88.4874	$88.49	$88.50	$88.50
Purchase #5	$49.40	9.490%	$54.0881	$54.09	$54.10	$54.10
Purchase #6	$51.85	5.688%	$54.7992	$54.80	$54.80	$54.80
Purchase #7	$191.35	7.245%	$205.2133	$205.21	$205.20	$205.20
7 purchase totals =	$782.96		$860.8189	$860.82	$860.85	$860.80