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	$36.95	8.392%	$40.0508	$40.05	$40.05	$40.10
Purchase #2	$234.81	7.759%	$253.0289	$253.03	$253.05	$253.00
Purchase #3	$52.54	8.375%	$56.9402	$56.94	$56.95	$56.90
Purchase #4	$57.77	7.834%	$62.2957	$62.30	$62.30	$62.30
Purchase #5	$58.38	12.679%	$65.782	$65.78	$65.80	$65.80
Purchase #6	$202.59	10.505%	$223.8721	$223.87	$223.85	$223.90
Purchase #7	$56.42	7.396%	$60.5928	$60.59	$60.60	$60.60
7 purchase totals =	$699.46		$762.5625	$762.56	$762.60	$762.60