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	$118.67	4.282%	$123.7514	$123.75	$123.75	$123.80
Purchase #2	$90.91	10.163%	$100.1492	$100.15	$100.15	$100.10
Purchase #3	$95.30	12.401%	$107.1182	$107.12	$107.10	$107.10
Purchase #4	$137.26	4.285%	$143.1416	$143.14	$143.15	$143.10
Purchase #5	$59.42	6.705%	$63.4041	$63.40	$63.40	$63.40
Purchase #6	$190.98	10.632%	$211.285	$211.29	$211.30	$211.30
Purchase #7	$220.71	9.329%	$241.3	$241.30	$241.30	$241.30
7 purchase totals =	$913.25		$990.1495	$990.15	$990.15	$990.10