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	$179.64	3.443%	$185.825	$185.83	$185.85	$185.80
Purchase #2	$164.65	8.803%	$179.1441	$179.14	$179.15	$179.10
Purchase #3	$104.25	13.582%	$118.4092	$118.41	$118.40	$118.40
Purchase #4	$140.90	10.401%	$155.555	$155.56	$155.55	$155.60
Purchase #5	$99.36	9.346%	$108.6462	$108.65	$108.65	$108.60
Purchase #6	$184.67	11.460%	$205.8332	$205.83	$205.85	$205.80
Purchase #7	$32.84	4.706%	$34.3855	$34.39	$34.40	$34.40
7 purchase totals =	$906.31		$987.7982	$987.81	$987.85	$987.70