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	$100.51	9.121%	$109.6775	$109.68	$109.70	$109.70
Purchase #2	$117.36	9.106%	$128.0468	$128.05	$128.05	$128.00
Purchase #3	$44.28	10.242%	$48.8152	$48.82	$48.80	$48.80
Purchase #4	$74.96	10.345%	$82.7146	$82.71	$82.70	$82.70
Purchase #5	$131.91	8.274%	$142.8242	$142.82	$142.80	$142.80
Purchase #6	$212.32	11.182%	$236.0616	$236.06	$236.05	$236.10
Purchase #7	$107.82	10.380%	$119.0117	$119.01	$119.00	$119.00
7 purchase totals =	$789.16		$867.1516	$867.15	$867.10	$867.10