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	$67.32	6.722%	$71.8453	$71.85	$71.85	$71.80
Purchase #2	$126.35	4.262%	$131.735	$131.74	$131.75	$131.70
Purchase #3	$73.91	12.622%	$83.2389	$83.24	$83.25	$83.20
Purchase #4	$154.47	3.865%	$160.4403	$160.44	$160.45	$160.40
Purchase #5	$177.70	8.823%	$193.3785	$193.38	$193.40	$193.40
Purchase #6	$83.42	6.198%	$88.5904	$88.59	$88.60	$88.60
Purchase #7	$99.79	9.683%	$109.4527	$109.45	$109.45	$109.50
7 purchase totals =	$782.96		$838.6811	$838.69	$838.75	$838.60