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	$57.78	9.352%	$63.1836	$63.18	$63.20	$63.20
Purchase #2	$102.97	6.670%	$109.8381	$109.84	$109.85	$109.80
Purchase #3	$123.27	13.228%	$139.5762	$139.58	$139.60	$139.60
Purchase #4	$206.32	13.232%	$233.6203	$233.62	$233.60	$233.60
Purchase #5	$80.69	13.862%	$91.8752	$91.88	$91.90	$91.90
Purchase #6	$10.37	13.550%	$11.7751	$11.78	$11.80	$11.80
Purchase #7	$192.64	13.340%	$218.3382	$218.34	$218.35	$218.30
7 purchase totals =	$774.04		$868.2067	$868.22	$868.30	$868.20