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	$140.90	12.236%	$158.1405	$158.14	$158.15	$158.10
Purchase #2	$142.28	3.660%	$147.4874	$147.49	$147.50	$147.50
Purchase #3	$57.88	4.379%	$60.4146	$60.41	$60.40	$60.40
Purchase #4	$21.48	13.695%	$24.4217	$24.42	$24.40	$24.40
Purchase #5	$229.64	11.396%	$255.8098	$255.81	$255.80	$255.80
Purchase #6	$87.96	12.356%	$98.8283	$98.83	$98.85	$98.80
Purchase #7	$173.65	7.381%	$186.4671	$186.47	$186.45	$186.50
7 purchase totals =	$853.79		$931.5694	$931.57	$931.55	$931.50