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	$60.25	10.474%	$66.5606	$66.56	$66.55	$66.60
Purchase #2	$85.84	6.279%	$91.2299	$91.23	$91.25	$91.20
Purchase #3	$151.90	9.382%	$166.1513	$166.15	$166.15	$166.20
Purchase #4	$92.49	11.325%	$102.9645	$102.96	$102.95	$103.00
Purchase #5	$74.64	11.730%	$83.3953	$83.40	$83.40	$83.40
Purchase #6	$61.62	9.189%	$67.2823	$67.28	$67.30	$67.30
Purchase #7	$141.59	6.108%	$150.2383	$150.24	$150.25	$150.20
7 purchase totals =	$668.33		$727.8222	$727.82	$727.85	$727.90