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	$20.35	4.630%	$21.2922	$21.29	$21.30	$21.30
Purchase #2	$103.53	7.865%	$111.6726	$111.67	$111.65	$111.70
Purchase #3	$10.73	6.616%	$11.4399	$11.44	$11.45	$11.40
Purchase #4	$105.51	13.737%	$120.0039	$120.00	$120.00	$120.00
Purchase #5	$181.93	5.320%	$191.6087	$191.61	$191.60	$191.60
Purchase #6	$184.64	3.300%	$190.7331	$190.73	$190.75	$190.70
Purchase #7	$16.49	11.352%	$18.3619	$18.36	$18.35	$18.40
7 purchase totals =	$623.18		$665.1123	$665.10	$665.10	$665.10