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	$90.66	9.455%	$99.2319	$99.23	$99.25	$99.20
Purchase #2	$209.79	10.454%	$231.7214	$231.72	$231.70	$231.70
Purchase #3	$67.72	12.666%	$76.2974	$76.30	$76.30	$76.30
Purchase #4	$97.91	7.393%	$105.1485	$105.15	$105.15	$105.10
Purchase #5	$224.36	11.698%	$250.6056	$250.61	$250.60	$250.60
Purchase #6	$22.65	13.500%	$25.7078	$25.71	$25.70	$25.70
Purchase #7	$56.83	3.436%	$58.7827	$58.78	$58.80	$58.80
7 purchase totals =	$769.92		$847.4953	$847.50	$847.50	$847.40