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	$60.35	4.171%	$62.8672	$62.87	$62.85	$62.90
Purchase #2	$77.67	11.649%	$86.7178	$86.72	$86.70	$86.70
Purchase #3	$82.44	9.200%	$90.0245	$90.02	$90.00	$90.00
Purchase #4	$162.56	10.310%	$179.3199	$179.32	$179.30	$179.30
Purchase #5	$85.45	6.256%	$90.7958	$90.80	$90.80	$90.80
Purchase #6	$91.29	11.154%	$101.4725	$101.47	$101.45	$101.50
Purchase #7	$150.38	12.307%	$168.8873	$168.89	$168.90	$168.90
7 purchase totals =	$710.14		$780.0850	$780.09	$780.00	$780.10