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	$77.62	5.412%	$81.8208	$81.82	$81.80	$81.80
Purchase #2	$192.51	11.791%	$215.2089	$215.21	$215.20	$215.20
Purchase #3	$91.61	12.818%	$103.3526	$103.35	$103.35	$103.40
Purchase #4	$228.50	11.142%	$253.9595	$253.96	$253.95	$254.00
Purchase #5	$140.36	10.533%	$155.1441	$155.14	$155.15	$155.10
Purchase #6	$104.46	6.844%	$111.6092	$111.61	$111.60	$111.60
Purchase #7	$131.63	9.115%	$143.6281	$143.63	$143.65	$143.60
7 purchase totals =	$966.69		$1,064.7232	$1,064.72	$1,064.70	$1,064.70