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	$42.74	4.224%	$44.5453	$44.55	$44.55	$44.50
Purchase #2	$25.69	9.316%	$28.0833	$28.08	$28.10	$28.10
Purchase #3	$100.27	11.298%	$111.5985	$111.60	$111.60	$111.60
Purchase #4	$84.84	10.545%	$93.7864	$93.79	$93.80	$93.80
Purchase #5	$126.84	3.596%	$131.4012	$131.40	$131.40	$131.40
Purchase #6	$165.82	6.212%	$176.1207	$176.12	$176.10	$176.10
Purchase #7	$123.56	6.332%	$131.3838	$131.38	$131.40	$131.40
7 purchase totals =	$669.76		$716.9192	$716.92	$716.95	$716.90