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	$91.35	10.477%	$100.9207	$100.92	$100.90	$100.90
Purchase #2	$22.83	6.720%	$24.3642	$24.36	$24.35	$24.40
Purchase #3	$179.50	3.307%	$185.4361	$185.44	$185.45	$185.40
Purchase #4	$204.92	5.660%	$216.5185	$216.52	$216.50	$216.50
Purchase #5	$14.73	5.118%	$15.4839	$15.48	$15.50	$15.50
Purchase #6	$141.81	3.628%	$146.9549	$146.95	$146.95	$147.00
Purchase #7	$246.50	8.685%	$267.9085	$267.91	$267.90	$267.90
7 purchase totals =	$901.64		$957.5868	$957.58	$957.55	$957.60