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	$138.89	12.686%	$156.5096	$156.51	$156.50	$156.50
Purchase #2	$136.94	4.443%	$143.0242	$143.02	$143.00	$143.00
Purchase #3	$67.38	6.413%	$71.7011	$71.70	$71.70	$71.70
Purchase #4	$51.60	3.855%	$53.5892	$53.59	$53.60	$53.60
Purchase #5	$182.80	4.857%	$191.6786	$191.68	$191.70	$191.70
Purchase #6	$224.28	13.784%	$255.1948	$255.19	$255.20	$255.20
Purchase #7	$249.26	8.506%	$270.4621	$270.46	$270.45	$270.50
7 purchase totals =	$1,051.15		$1,142.1596	$1,142.15	$1,142.15	$1,142.20