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	$41.82	8.552%	$45.3964	$45.40	$45.40	$45.40
Purchase #2	$133.51	13.567%	$151.6233	$151.62	$151.60	$151.60
Purchase #3	$208.90	11.592%	$233.1157	$233.12	$233.10	$233.10
Purchase #4	$111.73	10.326%	$123.2672	$123.27	$123.25	$123.30
Purchase #5	$180.85	11.463%	$201.5808	$201.58	$201.60	$201.60
Purchase #6	$148.74	6.104%	$157.8191	$157.82	$157.80	$157.80
Purchase #7	$161.38	3.757%	$167.443	$167.44	$167.45	$167.40
7 purchase totals =	$986.93		$1,080.2455	$1,080.25	$1,080.20	$1,080.20