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	$61.38	11.660%	$68.5369	$68.54	$68.55	$68.50
Purchase #2	$100.72	10.254%	$111.0478	$111.05	$111.05	$111.00
Purchase #3	$141.83	7.413%	$152.3439	$152.34	$152.35	$152.30
Purchase #4	$35.60	12.565%	$40.0731	$40.07	$40.05	$40.10
Purchase #5	$49.51	11.418%	$55.1631	$55.16	$55.15	$55.20
Purchase #6	$157.54	7.469%	$169.3067	$169.31	$169.30	$169.30
Purchase #7	$76.62	7.360%	$82.2592	$82.26	$82.25	$82.30
7 purchase totals =	$623.20		$678.7307	$678.73	$678.70	$678.70