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	$135.48	5.297%	$142.6564	$142.66	$142.65	$142.70
Purchase #2	$50.89	9.517%	$55.7332	$55.73	$55.75	$55.70
Purchase #3	$164.40	7.307%	$176.4127	$176.41	$176.40	$176.40
Purchase #4	$34.68	6.737%	$37.0164	$37.02	$37.00	$37.00
Purchase #5	$89.39	12.180%	$100.2777	$100.28	$100.30	$100.30
Purchase #6	$165.53	8.379%	$179.3998	$179.40	$179.40	$179.40
Purchase #7	$199.66	12.401%	$224.4198	$224.42	$224.40	$224.40
7 purchase totals =	$840.03		$915.9160	$915.92	$915.90	$915.90