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	$131.31	13.408%	$148.916	$148.92	$148.90	$148.90
Purchase #2	$74.42	4.235%	$77.5717	$77.57	$77.55	$77.60
Purchase #3	$67.43	9.320%	$73.7145	$73.71	$73.70	$73.70
Purchase #4	$36.43	13.710%	$41.4246	$41.42	$41.40	$41.40
Purchase #5	$93.79	5.250%	$98.714	$98.71	$98.70	$98.70
Purchase #6	$126.94	5.228%	$133.5764	$133.58	$133.60	$133.60
Purchase #7	$61.47	6.117%	$65.2301	$65.23	$65.25	$65.20
7 purchase totals =	$591.79		$639.1473	$639.14	$639.10	$639.10