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	$89.47	10.833%	$99.1623	$99.16	$99.15	$99.20
Purchase #2	$146.86	4.487%	$153.4496	$153.45	$153.45	$153.40
Purchase #3	$164.96	5.649%	$174.2786	$174.28	$174.30	$174.30
Purchase #4	$192.30	13.564%	$218.3836	$218.38	$218.40	$218.40
Purchase #5	$29.92	11.233%	$33.2809	$33.28	$33.30	$33.30
Purchase #6	$5.32	8.845%	$5.7906	$5.79	$5.80	$5.80
Purchase #7	$240.47	6.115%	$255.1747	$255.17	$255.15	$255.20
7 purchase totals =	$869.30		$939.5203	$939.51	$939.55	$939.60