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	$171.78	6.361%	$182.7069	$182.71	$182.70	$182.70
Purchase #2	$177.74	4.549%	$185.8254	$185.83	$185.85	$185.80
Purchase #3	$43.74	4.417%	$45.672	$45.67	$45.65	$45.70
Purchase #4	$173.83	4.331%	$181.3586	$181.36	$181.35	$181.40
Purchase #5	$92.43	10.863%	$102.4707	$102.47	$102.45	$102.50
Purchase #6	$18.86	5.745%	$19.9435	$19.94	$19.95	$19.90
Purchase #7	$105.52	7.216%	$113.1343	$113.13	$113.15	$113.10
7 purchase totals =	$783.90		$831.1114	$831.11	$831.10	$831.10