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	$45.33	13.651%	$51.518	$51.52	$51.50	$51.50
Purchase #2	$126.88	3.585%	$131.4286	$131.43	$131.45	$131.40
Purchase #3	$40.43	5.726%	$42.745	$42.75	$42.75	$42.70
Purchase #4	$155.49	6.856%	$166.1504	$166.15	$166.15	$166.20
Purchase #5	$191.56	3.533%	$198.3278	$198.33	$198.35	$198.30
Purchase #6	$141.25	10.784%	$156.4824	$156.48	$156.50	$156.50
Purchase #7	$31.45	3.252%	$32.4728	$32.47	$32.45	$32.50
7 purchase totals =	$732.39		$779.1250	$779.13	$779.15	$779.10