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	$103.42	5.490%	$109.0978	$109.10	$109.10	$109.10
Purchase #2	$79.82	13.536%	$90.6244	$90.62	$90.60	$90.60
Purchase #3	$97.68	5.422%	$102.9762	$102.98	$103.00	$103.00
Purchase #4	$96.93	12.395%	$108.9445	$108.94	$108.95	$108.90
Purchase #5	$82.70	10.553%	$91.4273	$91.43	$91.45	$91.40
Purchase #6	$145.76	13.241%	$165.0601	$165.06	$165.05	$165.10
Purchase #7	$167.90	10.355%	$185.286	$185.29	$185.30	$185.30
7 purchase totals =	$774.21		$853.4163	$853.42	$853.45	$853.40