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	$159.67	5.506%	$168.4614	$168.46	$168.45	$168.50
Purchase #2	$151.97	11.758%	$169.8386	$169.84	$169.85	$169.80
Purchase #3	$33.60	13.250%	$38.052	$38.05	$38.05	$38.10
Purchase #4	$204.72	9.782%	$224.7457	$224.75	$224.75	$224.70
Purchase #5	$74.83	5.445%	$78.9045	$78.90	$78.90	$78.90
Purchase #6	$185.91	7.264%	$199.4145	$199.41	$199.40	$199.40
Purchase #7	$74.44	12.170%	$83.4993	$83.50	$83.50	$83.50
7 purchase totals =	$885.14		$962.9160	$962.91	$962.90	$962.90