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	$90.91	12.351%	$102.1383	$102.14	$102.15	$102.10
Purchase #2	$237.56	5.416%	$250.4262	$250.43	$250.45	$250.40
Purchase #3	$151.49	13.447%	$171.8609	$171.86	$171.85	$171.90
Purchase #4	$130.42	9.222%	$142.4473	$142.45	$142.45	$142.40
Purchase #5	$118.27	7.390%	$127.0102	$127.01	$127.00	$127.00
Purchase #6	$153.26	8.818%	$166.7745	$166.77	$166.75	$166.80
Purchase #7	$195.92	5.395%	$206.4899	$206.49	$206.50	$206.50
7 purchase totals =	$1,077.83		$1,167.1473	$1,167.15	$1,167.15	$1,167.10