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	$179.31	7.835%	$193.3589	$193.36	$193.35	$193.40
Purchase #2	$27.41	13.533%	$31.1194	$31.12	$31.10	$31.10
Purchase #3	$159.40	5.367%	$167.955	$167.96	$167.95	$168.00
Purchase #4	$7.85	4.159%	$8.1765	$8.18	$8.20	$8.20
Purchase #5	$72.58	8.266%	$78.5795	$78.58	$78.60	$78.60
Purchase #6	$82.38	6.487%	$87.724	$87.72	$87.70	$87.70
Purchase #7	$69.55	3.758%	$72.1637	$72.16	$72.15	$72.20
7 purchase totals =	$598.48		$639.0770	$639.08	$639.05	$639.20