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	$25.86	9.629%	$28.3501	$28.35	$28.35	$28.40
Purchase #2	$51.66	5.181%	$54.3365	$54.34	$54.35	$54.30
Purchase #3	$54.61	13.494%	$61.9791	$61.98	$62.00	$62.00
Purchase #4	$38.52	8.624%	$41.842	$41.84	$41.85	$41.80
Purchase #5	$199.83	7.763%	$215.3428	$215.34	$215.35	$215.30
Purchase #6	$89.45	10.787%	$99.099	$99.10	$99.10	$99.10
Purchase #7	$75.65	5.376%	$79.7169	$79.72	$79.70	$79.70
7 purchase totals =	$535.58		$580.6664	$580.67	$580.70	$580.60