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	$78.46	13.287%	$88.885	$88.89	$88.90	$88.90
Purchase #2	$35.38	13.662%	$40.2136	$40.21	$40.20	$40.20
Purchase #3	$121.37	4.204%	$126.4724	$126.47	$126.45	$126.50
Purchase #4	$43.72	5.847%	$46.2763	$46.28	$46.30	$46.30
Purchase #5	$51.72	13.740%	$58.8263	$58.83	$58.85	$58.80
Purchase #6	$139.85	11.224%	$155.5468	$155.55	$155.55	$155.50
Purchase #7	$21.46	9.552%	$23.5099	$23.51	$23.50	$23.50
7 purchase totals =	$491.96		$539.7303	$539.74	$539.75	$539.70