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	$156.46	5.593%	$165.2108	$165.21	$165.20	$165.20
Purchase #2	$142.76	12.163%	$160.1239	$160.12	$160.10	$160.10
Purchase #3	$69.41	13.254%	$78.6096	$78.61	$78.60	$78.60
Purchase #4	$242.66	8.545%	$263.3953	$263.40	$263.40	$263.40
Purchase #5	$235.35	7.463%	$252.9142	$252.91	$252.90	$252.90
Purchase #6	$20.40	5.781%	$21.5793	$21.58	$21.60	$21.60
Purchase #7	$34.32	6.273%	$36.4729	$36.47	$36.45	$36.50
7 purchase totals =	$901.36		$978.3060	$978.30	$978.25	$978.30