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	$94.59	9.127%	$103.2232	$103.22	$103.20	$103.20
Purchase #2	$47.79	9.497%	$52.3286	$52.33	$52.35	$52.30
Purchase #3	$109.93	13.832%	$125.1355	$125.14	$125.15	$125.10
Purchase #4	$141.59	3.296%	$146.2568	$146.26	$146.25	$146.30
Purchase #5	$48.81	3.297%	$50.4193	$50.42	$50.40	$50.40
Purchase #6	$89.77	11.431%	$100.0316	$100.03	$100.05	$100.00
Purchase #7	$179.59	5.403%	$189.2932	$189.29	$189.30	$189.30
7 purchase totals =	$712.07		$766.6882	$766.69	$766.70	$766.60