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	$40.43	3.741%	$41.9425	$41.94	$41.95	$41.90
Purchase #2	$29.56	8.161%	$31.9724	$31.97	$31.95	$32.00
Purchase #3	$162.32	10.377%	$179.1639	$179.16	$179.15	$179.20
Purchase #4	$194.32	13.172%	$219.9158	$219.92	$219.90	$219.90
Purchase #5	$26.87	11.150%	$29.866	$29.87	$29.85	$29.90
Purchase #6	$40.75	3.407%	$42.1384	$42.14	$42.15	$42.10
Purchase #7	$146.60	12.564%	$165.0188	$165.02	$165.00	$165.00
7 purchase totals =	$640.85		$710.0178	$710.02	$709.95	$710.00