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	$131.85	5.690%	$139.3523	$139.35	$139.35	$139.40
Purchase #2	$105.94	10.152%	$116.695	$116.70	$116.70	$116.70
Purchase #3	$189.89	7.555%	$204.2362	$204.24	$204.25	$204.20
Purchase #4	$97.88	8.479%	$106.1792	$106.18	$106.20	$106.20
Purchase #5	$126.93	3.594%	$131.4919	$131.49	$131.50	$131.50
Purchase #6	$104.43	11.214%	$116.1408	$116.14	$116.15	$116.10
Purchase #7	$154.74	6.424%	$164.6805	$164.68	$164.70	$164.70
7 purchase totals =	$911.66		$978.7759	$978.78	$978.85	$978.80