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	$144.99	7.811%	$156.3152	$156.32	$156.30	$156.30
Purchase #2	$171.54	4.505%	$179.2679	$179.27	$179.25	$179.30
Purchase #3	$239.73	9.139%	$261.6389	$261.64	$261.65	$261.60
Purchase #4	$100.44	11.354%	$111.844	$111.84	$111.85	$111.80
Purchase #5	$18.28	3.121%	$18.8505	$18.85	$18.85	$18.90
Purchase #6	$87.45	13.348%	$99.1228	$99.12	$99.10	$99.10
Purchase #7	$227.86	13.211%	$257.9626	$257.96	$257.95	$258.00
7 purchase totals =	$990.29		$1,085.0019	$1,085.00	$1,084.95	$1,085.00