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	$108.84	10.315%	$120.0668	$120.07	$120.05	$120.10
Purchase #2	$121.91	7.874%	$131.5092	$131.51	$131.50	$131.50
Purchase #3	$86.55	6.839%	$92.4692	$92.47	$92.45	$92.50
Purchase #4	$75.96	10.796%	$84.1606	$84.16	$84.15	$84.20
Purchase #5	$143.46	10.461%	$158.4674	$158.47	$158.45	$158.50
Purchase #6	$7.88	12.296%	$8.8489	$8.85	$8.85	$8.80
Purchase #7	$82.64	8.132%	$89.3603	$89.36	$89.35	$89.40
7 purchase totals =	$627.24		$684.8824	$684.89	$684.80	$685.00