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	$153.27	3.660%	$158.8797	$158.88	$158.90	$158.90
Purchase #2	$244.79	13.812%	$278.6004	$278.60	$278.60	$278.60
Purchase #3	$131.98	7.159%	$141.4284	$141.43	$141.45	$141.40
Purchase #4	$123.70	4.406%	$129.1502	$129.15	$129.15	$129.20
Purchase #5	$245.29	9.627%	$268.9041	$268.90	$268.90	$268.90
Purchase #6	$160.59	10.785%	$177.9096	$177.91	$177.90	$177.90
Purchase #7	$6.55	13.223%	$7.4161	$7.42	$7.40	$7.40
7 purchase totals =	$1,066.17		$1,162.2885	$1,162.29	$1,162.30	$1,162.30