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	$51.43	6.581%	$54.8146	$54.81	$54.80	$54.80
Purchase #2	$133.40	9.436%	$145.9876	$145.99	$146.00	$146.00
Purchase #3	$85.26	13.131%	$96.4555	$96.46	$96.45	$96.50
Purchase #4	$50.44	9.226%	$55.0936	$55.09	$55.10	$55.10
Purchase #5	$85.25	12.616%	$96.0051	$96.01	$96.00	$96.00
Purchase #6	$65.29	11.213%	$72.611	$72.61	$72.60	$72.60
Purchase #7	$158.98	5.131%	$167.1373	$167.14	$167.15	$167.10
7 purchase totals =	$630.05		$688.1047	$688.11	$688.10	$688.10