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	$122.91	3.589%	$127.3212	$127.32	$127.30	$127.30
Purchase #2	$26.94	6.237%	$28.6202	$28.62	$28.60	$28.60
Purchase #3	$213.68	12.420%	$240.2191	$240.22	$240.20	$240.20
Purchase #4	$249.48	4.421%	$260.5095	$260.51	$260.50	$260.50
Purchase #5	$100.60	8.692%	$109.3442	$109.34	$109.35	$109.30
Purchase #6	$39.62	11.865%	$44.3209	$44.32	$44.30	$44.30
Purchase #7	$94.88	10.797%	$105.1242	$105.12	$105.10	$105.10
7 purchase totals =	$848.11		$915.4593	$915.45	$915.35	$915.30