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	$50.71	10.105%	$55.8342	$55.83	$55.85	$55.80
Purchase #2	$48.79	7.763%	$52.5776	$52.58	$52.60	$52.60
Purchase #3	$60.48	8.496%	$65.6184	$65.62	$65.60	$65.60
Purchase #4	$101.86	7.121%	$109.1135	$109.11	$109.10	$109.10
Purchase #5	$194.75	7.453%	$209.2647	$209.26	$209.25	$209.30
Purchase #6	$69.54	13.427%	$78.8771	$78.88	$78.90	$78.90
Purchase #7	$102.62	8.430%	$111.2709	$111.27	$111.25	$111.30
7 purchase totals =	$628.75		$682.5564	$682.55	$682.55	$682.60