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	$61.56	6.121%	$65.3281	$65.33	$65.35	$65.30
Purchase #2	$225.90	7.773%	$243.4592	$243.46	$243.45	$243.50
Purchase #3	$212.86	3.851%	$221.0572	$221.06	$221.05	$221.10
Purchase #4	$111.33	7.443%	$119.6163	$119.62	$119.60	$119.60
Purchase #5	$34.66	10.196%	$38.1939	$38.19	$38.20	$38.20
Purchase #6	$149.25	10.389%	$164.7556	$164.76	$164.75	$164.80
Purchase #7	$123.52	5.856%	$130.7533	$130.75	$130.75	$130.80
7 purchase totals =	$919.08		$983.1636	$983.17	$983.15	$983.30