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	$176.54	8.435%	$191.4311	$191.43	$191.45	$191.40
Purchase #2	$193.81	3.260%	$200.1282	$200.13	$200.15	$200.10
Purchase #3	$47.35	9.785%	$51.9832	$51.98	$52.00	$52.00
Purchase #4	$234.45	8.191%	$253.6538	$253.65	$253.65	$253.70
Purchase #5	$33.46	12.508%	$37.6452	$37.65	$37.65	$37.60
Purchase #6	$24.53	12.517%	$27.6004	$27.60	$27.60	$27.60
Purchase #7	$72.87	6.366%	$77.5089	$77.51	$77.50	$77.50
7 purchase totals =	$783.01		$839.9508	$839.95	$840.00	$839.90