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	$30.65	5.461%	$32.3238	$32.32	$32.30	$32.30
Purchase #2	$196.55	6.530%	$209.3847	$209.38	$209.40	$209.40
Purchase #3	$82.69	8.208%	$89.4772	$89.48	$89.50	$89.50
Purchase #4	$38.39	7.276%	$41.1833	$41.18	$41.20	$41.20
Purchase #5	$158.59	5.139%	$166.7399	$166.74	$166.75	$166.70
Purchase #6	$14.95	7.314%	$16.0434	$16.04	$16.05	$16.00
Purchase #7	$91.79	12.735%	$103.4795	$103.48	$103.50	$103.50
7 purchase totals =	$613.61		$658.6318	$658.62	$658.70	$658.60