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	$246.41	8.777%	$268.0374	$268.04	$268.05	$268.00
Purchase #2	$224.25	3.375%	$231.8184	$231.82	$231.80	$231.80
Purchase #3	$48.28	8.689%	$52.475	$52.48	$52.50	$52.50
Purchase #4	$61.88	13.570%	$70.2771	$70.28	$70.30	$70.30
Purchase #5	$7.41	3.152%	$7.6436	$7.64	$7.65	$7.60
Purchase #6	$8.67	10.566%	$9.5861	$9.59	$9.60	$9.60
Purchase #7	$52.57	13.608%	$59.7237	$59.72	$59.70	$59.70
7 purchase totals =	$649.47		$699.5613	$699.57	$699.60	$699.50