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	$18.52	9.186%	$20.2212	$20.22	$20.20	$20.20
Purchase #2	$164.75	11.437%	$183.5925	$183.59	$183.60	$183.60
Purchase #3	$89.58	6.480%	$95.3848	$95.38	$95.40	$95.40
Purchase #4	$134.91	4.864%	$141.472	$141.47	$141.45	$141.50
Purchase #5	$77.32	7.381%	$83.027	$83.03	$83.05	$83.00
Purchase #6	$52.88	4.776%	$55.4055	$55.41	$55.40	$55.40
Purchase #7	$29.31	9.326%	$32.0435	$32.04	$32.05	$32.00
7 purchase totals =	$567.27		$611.1465	$611.14	$611.15	$611.10