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	$245.71	4.204%	$256.0396	$256.04	$256.05	$256.00
Purchase #2	$162.31	9.152%	$177.1646	$177.16	$177.15	$177.20
Purchase #3	$181.82	11.176%	$202.1402	$202.14	$202.15	$202.10
Purchase #4	$90.63	5.764%	$95.8539	$95.85	$95.85	$95.90
Purchase #5	$65.92	8.375%	$71.4408	$71.44	$71.45	$71.40
Purchase #6	$134.98	4.726%	$141.3592	$141.36	$141.35	$141.40
Purchase #7	$30.78	13.267%	$34.8636	$34.86	$34.85	$34.90
7 purchase totals =	$912.15		$978.8619	$978.85	$978.85	$978.90