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	$139.60	11.673%	$155.8955	$155.90	$155.90	$155.90
Purchase #2	$42.81	13.497%	$48.5881	$48.59	$48.60	$48.60
Purchase #3	$193.58	11.599%	$216.0333	$216.03	$216.05	$216.00
Purchase #4	$153.66	13.317%	$174.1229	$174.12	$174.10	$174.10
Purchase #5	$99.97	3.332%	$103.301	$103.30	$103.30	$103.30
Purchase #6	$144.66	3.820%	$150.186	$150.19	$150.20	$150.20
Purchase #7	$144.31	10.701%	$159.7526	$159.75	$159.75	$159.80
7 purchase totals =	$918.59		$1,007.8794	$1,007.88	$1,007.90	$1,007.90