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	$153.78	11.762%	$171.8676	$171.87	$171.85	$171.90
Purchase #2	$79.72	12.137%	$89.3956	$89.40	$89.40	$89.40
Purchase #3	$138.95	4.651%	$145.4126	$145.41	$145.40	$145.40
Purchase #4	$63.54	5.282%	$66.8962	$66.90	$66.90	$66.90
Purchase #5	$168.79	8.782%	$183.6131	$183.61	$183.60	$183.60
Purchase #6	$61.70	12.589%	$69.4674	$69.47	$69.45	$69.50
Purchase #7	$157.47	4.766%	$164.975	$164.98	$165.00	$165.00
7 purchase totals =	$823.95		$891.6275	$891.64	$891.60	$891.70