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	$155.31	7.451%	$166.8821	$166.88	$166.90	$166.90
Purchase #2	$205.75	11.373%	$229.1499	$229.15	$229.15	$229.10
Purchase #3	$38.61	12.836%	$43.566	$43.57	$43.55	$43.60
Purchase #4	$28.61	9.425%	$31.3065	$31.31	$31.30	$31.30
Purchase #5	$134.67	8.251%	$145.7816	$145.78	$145.80	$145.80
Purchase #6	$16.59	10.527%	$18.3364	$18.34	$18.35	$18.30
Purchase #7	$93.50	11.115%	$103.8925	$103.89	$103.90	$103.90
7 purchase totals =	$673.04		$738.9150	$738.92	$738.95	$738.90