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	$201.49	9.780%	$221.1957	$221.20	$221.20	$221.20
Purchase #2	$54.28	6.575%	$57.8489	$57.85	$57.85	$57.80
Purchase #3	$212.39	4.146%	$221.1957	$221.20	$221.20	$221.20
Purchase #4	$56.61	8.511%	$61.4281	$61.43	$61.45	$61.40
Purchase #5	$59.40	11.706%	$66.3534	$66.35	$66.35	$66.40
Purchase #6	$56.42	4.793%	$59.1242	$59.12	$59.10	$59.10
Purchase #7	$71.44	9.213%	$78.0218	$78.02	$78.00	$78.00
7 purchase totals =	$712.03		$765.1678	$765.17	$765.15	$765.10