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	$143.32	4.825%	$150.2352	$150.24	$150.25	$150.20
Purchase #2	$154.30	6.828%	$164.8356	$164.84	$164.85	$164.80
Purchase #3	$37.87	10.329%	$41.7816	$41.78	$41.80	$41.80
Purchase #4	$53.43	7.417%	$57.3929	$57.39	$57.40	$57.40
Purchase #5	$7.38	7.278%	$7.9171	$7.92	$7.90	$7.90
Purchase #6	$52.46	5.398%	$55.2918	$55.29	$55.30	$55.30
Purchase #7	$155.42	3.583%	$160.9887	$160.99	$161.00	$161.00
7 purchase totals =	$604.18		$638.4429	$638.45	$638.50	$638.40