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	$111.37	4.701%	$116.6055	$116.61	$116.60	$116.60
Purchase #2	$40.70	5.214%	$42.8221	$42.82	$42.80	$42.80
Purchase #3	$25.97	12.494%	$29.2147	$29.21	$29.20	$29.20
Purchase #4	$221.73	12.369%	$249.1558	$249.16	$249.15	$249.20
Purchase #5	$88.47	8.278%	$95.7935	$95.79	$95.80	$95.80
Purchase #6	$76.30	6.580%	$81.3205	$81.32	$81.30	$81.30
Purchase #7	$33.78	4.321%	$35.2396	$35.24	$35.25	$35.20
7 purchase totals =	$598.32		$650.1517	$650.15	$650.10	$650.10