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	$158.50	6.387%	$168.6234	$168.62	$168.60	$168.60
Purchase #2	$103.26	3.248%	$106.6139	$106.61	$106.60	$106.60
Purchase #3	$31.76	5.587%	$33.5344	$33.53	$33.55	$33.50
Purchase #4	$75.90	4.383%	$79.2267	$79.23	$79.25	$79.20
Purchase #5	$86.78	4.464%	$90.6539	$90.65	$90.65	$90.70
Purchase #6	$164.94	13.841%	$187.7693	$187.77	$187.75	$187.80
Purchase #7	$160.54	7.781%	$173.0316	$173.03	$173.05	$173.00
7 purchase totals =	$781.68		$839.4532	$839.44	$839.45	$839.40