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	$30.39	11.726%	$33.9535	$33.95	$33.95	$34.00
Purchase #2	$127.53	9.318%	$139.4132	$139.41	$139.40	$139.40
Purchase #3	$175.45	6.153%	$186.2454	$186.25	$186.25	$186.20
Purchase #4	$243.26	10.820%	$269.5807	$269.58	$269.60	$269.60
Purchase #5	$10.75	5.499%	$11.3411	$11.34	$11.35	$11.30
Purchase #6	$71.56	9.849%	$78.6079	$78.61	$78.60	$78.60
Purchase #7	$209.53	13.469%	$237.7516	$237.75	$237.75	$237.80
7 purchase totals =	$868.47		$956.8934	$956.89	$956.90	$956.90