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	$118.25	12.245%	$132.7297	$132.73	$132.75	$132.70
Purchase #2	$179.81	6.411%	$191.3376	$191.34	$191.35	$191.30
Purchase #3	$116.58	10.584%	$128.9188	$128.92	$128.90	$128.90
Purchase #4	$191.40	4.438%	$199.8943	$199.89	$199.90	$199.90
Purchase #5	$20.77	3.289%	$21.4531	$21.45	$21.45	$21.50
Purchase #6	$98.45	11.586%	$109.8564	$109.86	$109.85	$109.90
Purchase #7	$43.82	11.766%	$48.9759	$48.98	$49.00	$49.00
7 purchase totals =	$769.08		$833.1658	$833.17	$833.20	$833.20