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	$36.45	8.116%	$39.4083	$39.41	$39.40	$39.40
Purchase #2	$94.54	11.107%	$105.0406	$105.04	$105.05	$105.00
Purchase #3	$28.52	7.718%	$30.7212	$30.72	$30.70	$30.70
Purchase #4	$37.91	10.746%	$41.9838	$41.98	$42.00	$42.00
Purchase #5	$140.72	9.333%	$153.8534	$153.85	$153.85	$153.90
Purchase #6	$133.34	6.247%	$141.6697	$141.67	$141.65	$141.70
Purchase #7	$97.30	12.683%	$109.6406	$109.64	$109.65	$109.60
7 purchase totals =	$568.78		$622.3176	$622.31	$622.30	$622.30