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	$202.55	3.152%	$208.9344	$208.93	$208.95	$208.90
Purchase #2	$244.77	9.141%	$267.1444	$267.14	$267.15	$267.10
Purchase #3	$77.58	3.633%	$80.3985	$80.40	$80.40	$80.40
Purchase #4	$149.69	7.470%	$160.8718	$160.87	$160.85	$160.90
Purchase #5	$117.49	11.863%	$131.4278	$131.43	$131.45	$131.40
Purchase #6	$96.65	12.589%	$108.8173	$108.82	$108.80	$108.80
Purchase #7	$197.65	12.614%	$222.5816	$222.58	$222.60	$222.60
7 purchase totals =	$1,086.38		$1,180.1758	$1,180.17	$1,180.20	$1,180.10