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	$210.83	13.256%	$238.7776	$238.78	$238.80	$238.80
Purchase #2	$145.31	8.849%	$158.1685	$158.17	$158.15	$158.20
Purchase #3	$250.68	5.148%	$263.585	$263.59	$263.60	$263.60
Purchase #4	$83.42	6.688%	$88.9991	$89.00	$89.00	$89.00
Purchase #5	$50.58	4.541%	$52.8768	$52.88	$52.90	$52.90
Purchase #6	$243.79	7.824%	$262.8641	$262.86	$262.85	$262.90
Purchase #7	$104.51	13.678%	$118.8049	$118.80	$118.80	$118.80
7 purchase totals =	$1,089.12		$1,184.0760	$1,184.08	$1,184.10	$1,184.20