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	$249.43	8.766%	$271.295	$271.30	$271.30	$271.30
Purchase #2	$33.83	12.329%	$38.0009	$38.00	$38.00	$38.00
Purchase #3	$18.94	8.393%	$20.5296	$20.53	$20.55	$20.50
Purchase #4	$18.42	11.369%	$20.5142	$20.51	$20.50	$20.50
Purchase #5	$196.93	4.648%	$206.0833	$206.08	$206.10	$206.10
Purchase #6	$114.25	7.718%	$123.0678	$123.07	$123.05	$123.10
Purchase #7	$106.47	9.166%	$116.229	$116.23	$116.25	$116.20
7 purchase totals =	$738.27		$795.7198	$795.72	$795.75	$795.70