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	$151.51	5.318%	$159.5673	$159.57	$159.55	$159.60
Purchase #2	$77.89	4.601%	$81.4737	$81.47	$81.45	$81.50
Purchase #3	$66.86	6.366%	$71.1163	$71.12	$71.10	$71.10
Purchase #4	$74.80	7.172%	$80.1647	$80.16	$80.15	$80.20
Purchase #5	$131.97	8.227%	$142.8272	$142.83	$142.85	$142.80
Purchase #6	$10.82	4.656%	$11.3238	$11.32	$11.30	$11.30
Purchase #7	$111.46	13.807%	$126.8493	$126.85	$126.85	$126.80
7 purchase totals =	$625.31		$673.3223	$673.32	$673.25	$673.30