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	$222.32	6.203%	$236.1105	$236.11	$236.10	$236.10
Purchase #2	$68.46	4.319%	$71.4168	$71.42	$71.40	$71.40
Purchase #3	$32.66	4.486%	$34.1251	$34.13	$34.15	$34.10
Purchase #4	$103.82	12.648%	$116.9512	$116.95	$116.95	$117.00
Purchase #5	$37.93	13.746%	$43.1439	$43.14	$43.15	$43.10
Purchase #6	$76.57	7.280%	$82.1443	$82.14	$82.15	$82.10
Purchase #7	$73.75	9.168%	$80.5114	$80.51	$80.50	$80.50
7 purchase totals =	$615.51		$664.4032	$664.40	$664.40	$664.30