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	$89.59	10.571%	$99.0606	$99.06	$99.05	$99.10
Purchase #2	$162.88	9.275%	$177.9871	$177.99	$178.00	$178.00
Purchase #3	$213.39	4.386%	$222.7493	$222.75	$222.75	$222.70
Purchase #4	$189.46	12.578%	$213.2903	$213.29	$213.30	$213.30
Purchase #5	$44.50	11.298%	$49.5276	$49.53	$49.55	$49.50
Purchase #6	$79.65	4.333%	$83.1012	$83.10	$83.10	$83.10
Purchase #7	$97.25	8.269%	$105.2916	$105.29	$105.30	$105.30
7 purchase totals =	$876.72		$951.0077	$951.01	$951.05	$951.00