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	$80.33	3.138%	$82.8508	$82.85	$82.85	$82.90
Purchase #2	$50.77	10.104%	$55.8998	$55.90	$55.90	$55.90
Purchase #3	$103.69	12.325%	$116.4698	$116.47	$116.45	$116.50
Purchase #4	$212.84	3.655%	$220.6193	$220.62	$220.60	$220.60
Purchase #5	$80.76	5.464%	$85.1727	$85.17	$85.15	$85.20
Purchase #6	$74.28	3.513%	$76.8895	$76.89	$76.90	$76.90
Purchase #7	$41.43	10.832%	$45.9177	$45.92	$45.90	$45.90
7 purchase totals =	$644.10		$683.8196	$683.82	$683.75	$683.90