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	$104.80	3.230%	$108.185	$108.19	$108.20	$108.20
Purchase #2	$49.78	6.833%	$53.1815	$53.18	$53.20	$53.20
Purchase #3	$95.96	13.826%	$109.2274	$109.23	$109.25	$109.20
Purchase #4	$74.80	8.627%	$81.253	$81.25	$81.25	$81.30
Purchase #5	$85.41	4.629%	$89.3636	$89.36	$89.35	$89.40
Purchase #6	$9.85	8.850%	$10.7217	$10.72	$10.70	$10.70
Purchase #7	$7.31	10.526%	$8.0795	$8.08	$8.10	$8.10
7 purchase totals =	$427.91		$460.0117	$460.01	$460.05	$460.10