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	$31.31	8.155%	$33.8633	$33.86	$33.85	$33.90
Purchase #2	$149.32	4.613%	$156.2081	$156.21	$156.20	$156.20
Purchase #3	$170.85	3.502%	$176.8332	$176.83	$176.85	$176.80
Purchase #4	$22.32	10.858%	$24.7435	$24.74	$24.75	$24.70
Purchase #5	$31.51	12.779%	$35.5367	$35.54	$35.55	$35.50
Purchase #6	$250.52	11.497%	$279.3223	$279.32	$279.30	$279.30
Purchase #7	$221.30	12.768%	$249.5556	$249.56	$249.55	$249.60
7 purchase totals =	$877.13		$956.0627	$956.06	$956.05	$956.00