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	$78.80	6.193%	$83.6801	$83.68	$83.70	$83.70
Purchase #2	$185.28	10.575%	$204.8734	$204.87	$204.85	$204.90
Purchase #3	$55.75	7.237%	$59.7846	$59.78	$59.80	$59.80
Purchase #4	$135.57	3.200%	$139.9082	$139.91	$139.90	$139.90
Purchase #5	$93.29	8.215%	$100.9538	$100.95	$100.95	$101.00
Purchase #6	$94.43	5.723%	$99.8342	$99.83	$99.85	$99.80
Purchase #7	$83.81	7.225%	$89.8653	$89.87	$89.85	$89.90
7 purchase totals =	$726.93		$778.8996	$778.89	$778.90	$779.00