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	$36.68	7.145%	$39.3008	$39.30	$39.30	$39.30
Purchase #2	$30.37	3.575%	$31.4557	$31.46	$31.45	$31.50
Purchase #3	$245.25	4.420%	$256.0901	$256.09	$256.10	$256.10
Purchase #4	$31.42	9.361%	$34.3612	$34.36	$34.35	$34.40
Purchase #5	$181.82	4.425%	$189.8655	$189.87	$189.85	$189.90
Purchase #6	$215.42	6.574%	$229.5817	$229.58	$229.60	$229.60
Purchase #7	$38.58	10.534%	$42.644	$42.64	$42.65	$42.60
7 purchase totals =	$779.54		$823.2990	$823.30	$823.30	$823.40