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	$88.27	13.197%	$99.919	$99.92	$99.90	$99.90
Purchase #2	$168.47	7.665%	$181.3832	$181.38	$181.40	$181.40
Purchase #3	$100.61	13.250%	$113.9408	$113.94	$113.95	$113.90
Purchase #4	$28.74	13.322%	$32.5687	$32.57	$32.55	$32.60
Purchase #5	$126.94	4.120%	$132.1699	$132.17	$132.15	$132.20
Purchase #6	$67.29	5.491%	$70.9849	$70.98	$71.00	$71.00
Purchase #7	$180.87	9.158%	$197.4341	$197.43	$197.45	$197.40
7 purchase totals =	$761.19		$828.4006	$828.39	$828.40	$828.40