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	$142.92	11.574%	$159.4616	$159.46	$159.45	$159.50
Purchase #2	$30.97	11.232%	$34.4486	$34.45	$34.45	$34.40
Purchase #3	$131.48	9.431%	$143.8799	$143.88	$143.90	$143.90
Purchase #4	$27.63	4.206%	$28.7921	$28.79	$28.80	$28.80
Purchase #5	$156.64	5.688%	$165.5497	$165.55	$165.55	$165.50
Purchase #6	$94.32	13.254%	$106.8212	$106.82	$106.80	$106.80
Purchase #7	$216.48	5.852%	$229.1484	$229.15	$229.15	$229.10
7 purchase totals =	$800.44		$868.1015	$868.10	$868.10	$868.00