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	$46.61	8.507%	$50.5751	$50.58	$50.60	$50.60
Purchase #2	$84.39	4.573%	$88.2492	$88.25	$88.25	$88.20
Purchase #3	$38.77	5.252%	$40.8062	$40.81	$40.80	$40.80
Purchase #4	$112.25	11.443%	$125.0948	$125.09	$125.10	$125.10
Purchase #5	$204.27	5.363%	$215.225	$215.23	$215.25	$215.20
Purchase #6	$82.52	9.639%	$90.4741	$90.47	$90.45	$90.50
Purchase #7	$140.92	12.501%	$158.5364	$158.54	$158.55	$158.50
7 purchase totals =	$709.73		$768.9608	$768.97	$769.00	$768.90