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	$142.46	11.459%	$158.7845	$158.78	$158.80	$158.80
Purchase #2	$60.89	9.140%	$66.4553	$66.46	$66.45	$66.50
Purchase #3	$110.83	11.408%	$123.4735	$123.47	$123.45	$123.50
Purchase #4	$183.47	10.427%	$202.6004	$202.60	$202.60	$202.60
Purchase #5	$166.82	13.753%	$189.7628	$189.76	$189.75	$189.80
Purchase #6	$210.97	8.835%	$229.6092	$229.61	$229.60	$229.60
Purchase #7	$108.39	9.442%	$118.6242	$118.62	$118.60	$118.60
7 purchase totals =	$983.83		$1,089.3099	$1,089.30	$1,089.25	$1,089.40