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	$131.46	8.387%	$142.4856	$142.49	$142.50	$142.50
Purchase #2	$123.75	3.128%	$127.6209	$127.62	$127.60	$127.60
Purchase #3	$181.42	12.572%	$204.2281	$204.23	$204.25	$204.20
Purchase #4	$90.97	13.473%	$103.2264	$103.23	$103.25	$103.20
Purchase #5	$118.47	11.298%	$131.8547	$131.85	$131.85	$131.90
Purchase #6	$202.90	12.425%	$228.1103	$228.11	$228.10	$228.10
Purchase #7	$141.67	8.244%	$153.3493	$153.35	$153.35	$153.30
7 purchase totals =	$990.64		$1,090.8753	$1,090.88	$1,090.90	$1,090.80