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	$164.53	3.866%	$170.8907	$170.89	$170.90	$170.90
Purchase #2	$164.29	9.498%	$179.8943	$179.89	$179.90	$179.90
Purchase #3	$165.83	11.274%	$184.5257	$184.53	$184.55	$184.50
Purchase #4	$193.28	4.142%	$201.2857	$201.29	$201.30	$201.30
Purchase #5	$76.43	7.642%	$82.2708	$82.27	$82.25	$82.30
Purchase #6	$32.59	5.188%	$34.2808	$34.28	$34.30	$34.30
Purchase #7	$116.45	10.390%	$128.5492	$128.55	$128.55	$128.50
7 purchase totals =	$913.40		$981.6972	$981.70	$981.75	$981.70