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	$180.57	12.748%	$203.5891	$203.59	$203.60	$203.60
Purchase #2	$208.64	6.799%	$222.8254	$222.83	$222.85	$222.80
Purchase #3	$115.92	6.802%	$123.8049	$123.80	$123.80	$123.80
Purchase #4	$141.84	10.326%	$156.4864	$156.49	$156.50	$156.50
Purchase #5	$46.69	13.132%	$52.8213	$52.82	$52.80	$52.80
Purchase #6	$241.99	13.673%	$275.0773	$275.08	$275.10	$275.10
Purchase #7	$114.31	8.141%	$123.616	$123.62	$123.60	$123.60
7 purchase totals =	$1,049.96		$1,158.2204	$1,158.23	$1,158.25	$1,158.20