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	$87.66	13.460%	$99.459	$99.46	$99.45	$99.50
Purchase #2	$130.91	9.841%	$143.7929	$143.79	$143.80	$143.80
Purchase #3	$35.46	9.713%	$38.9042	$38.90	$38.90	$38.90
Purchase #4	$19.58	3.788%	$20.3217	$20.32	$20.30	$20.30
Purchase #5	$244.82	11.169%	$272.1639	$272.16	$272.15	$272.20
Purchase #6	$52.83	12.731%	$59.5558	$59.56	$59.55	$59.60
Purchase #7	$150.29	3.520%	$155.5802	$155.58	$155.60	$155.60
7 purchase totals =	$721.55		$789.7777	$789.77	$789.75	$789.90