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	$117.57	9.387%	$128.6063	$128.61	$128.60	$128.60
Purchase #2	$90.61	3.448%	$93.7342	$93.73	$93.75	$93.70
Purchase #3	$29.50	8.482%	$32.0022	$32.00	$32.00	$32.00
Purchase #4	$18.45	11.582%	$20.5869	$20.59	$20.60	$20.60
Purchase #5	$37.59	6.628%	$40.0815	$40.08	$40.10	$40.10
Purchase #6	$174.65	12.144%	$195.8595	$195.86	$195.85	$195.90
Purchase #7	$18.48	6.772%	$19.7315	$19.73	$19.75	$19.70
7 purchase totals =	$486.85		$530.6021	$530.60	$530.65	$530.60