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	$90.80	9.856%	$99.7492	$99.75	$99.75	$99.70
Purchase #2	$140.90	8.246%	$152.5186	$152.52	$152.50	$152.50
Purchase #3	$98.90	3.215%	$102.0796	$102.08	$102.10	$102.10
Purchase #4	$134.42	3.761%	$139.4755	$139.48	$139.50	$139.50
Purchase #5	$226.51	10.676%	$250.6922	$250.69	$250.70	$250.70
Purchase #6	$153.94	11.746%	$172.0218	$172.02	$172.00	$172.00
Purchase #7	$17.47	5.406%	$18.4144	$18.41	$18.40	$18.40
7 purchase totals =	$862.94		$934.9513	$934.95	$934.95	$934.90