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	$55.77	7.221%	$59.7972	$59.80	$59.80	$59.80
Purchase #2	$209.83	4.395%	$219.052	$219.05	$219.05	$219.10
Purchase #3	$14.80	13.480%	$16.795	$16.80	$16.80	$16.80
Purchase #4	$217.64	5.739%	$230.1304	$230.13	$230.15	$230.10
Purchase #5	$35.47	9.156%	$38.7176	$38.72	$38.70	$38.70
Purchase #6	$103.95	7.689%	$111.9427	$111.94	$111.95	$111.90
Purchase #7	$201.90	9.649%	$221.3813	$221.38	$221.40	$221.40
7 purchase totals =	$839.36		$897.8162	$897.82	$897.85	$897.80