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	$79.58	12.484%	$89.5148	$89.51	$89.50	$89.50
Purchase #2	$161.73	7.683%	$174.1557	$174.16	$174.15	$174.20
Purchase #3	$21.26	5.727%	$22.4776	$22.48	$22.50	$22.50
Purchase #4	$117.28	10.515%	$129.612	$129.61	$129.60	$129.60
Purchase #5	$244.54	7.306%	$262.4061	$262.41	$262.40	$262.40
Purchase #6	$111.32	7.249%	$119.3896	$119.39	$119.40	$119.40
Purchase #7	$123.58	6.153%	$131.1839	$131.18	$131.20	$131.20
7 purchase totals =	$859.29		$928.7397	$928.74	$928.75	$928.80