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	$41.97	12.664%	$47.2851	$47.29	$47.30	$47.30
Purchase #2	$71.93	5.412%	$75.8229	$75.82	$75.80	$75.80
Purchase #3	$177.34	10.684%	$196.287	$196.29	$196.30	$196.30
Purchase #4	$174.91	3.563%	$181.142	$181.14	$181.15	$181.10
Purchase #5	$48.96	4.821%	$51.3204	$51.32	$51.30	$51.30
Purchase #6	$127.75	13.518%	$145.0192	$145.02	$145.00	$145.00
Purchase #7	$99.43	9.852%	$109.2258	$109.23	$109.25	$109.20
7 purchase totals =	$742.29		$806.1024	$806.11	$806.10	$806.00