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	$77.99	3.685%	$80.8639	$80.86	$80.85	$80.90
Purchase #2	$94.49	6.619%	$100.7443	$100.74	$100.75	$100.70
Purchase #3	$184.86	13.373%	$209.5813	$209.58	$209.60	$209.60
Purchase #4	$78.43	5.505%	$82.7476	$82.75	$82.75	$82.70
Purchase #5	$229.34	10.443%	$253.29	$253.29	$253.30	$253.30
Purchase #6	$75.52	3.846%	$78.4245	$78.42	$78.40	$78.40
Purchase #7	$125.80	12.830%	$141.9401	$141.94	$141.95	$141.90
7 purchase totals =	$866.43		$947.5917	$947.58	$947.60	$947.50