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	$179.82	4.352%	$187.6458	$187.65	$187.65	$187.60
Purchase #2	$24.97	8.826%	$27.1739	$27.17	$27.15	$27.20
Purchase #3	$143.50	11.429%	$159.9006	$159.90	$159.90	$159.90
Purchase #4	$241.25	3.706%	$250.1907	$250.19	$250.20	$250.20
Purchase #5	$227.26	3.803%	$235.9027	$235.90	$235.90	$235.90
Purchase #6	$50.51	5.525%	$53.3007	$53.30	$53.30	$53.30
Purchase #7	$52.97	4.647%	$55.4315	$55.43	$55.45	$55.40
7 purchase totals =	$920.28		$969.5459	$969.54	$969.55	$969.50