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	$99.93	11.739%	$111.6608	$111.66	$111.65	$111.70
Purchase #2	$226.42	9.615%	$248.1903	$248.19	$248.20	$248.20
Purchase #3	$242.55	7.370%	$260.4259	$260.43	$260.45	$260.40
Purchase #4	$213.45	4.810%	$223.7169	$223.72	$223.70	$223.70
Purchase #5	$96.66	12.450%	$108.6942	$108.69	$108.70	$108.70
Purchase #6	$78.35	8.687%	$85.1563	$85.16	$85.15	$85.20
Purchase #7	$28.79	12.253%	$32.3176	$32.32	$32.30	$32.30
7 purchase totals =	$986.15		$1,070.1620	$1,070.17	$1,070.15	$1,070.20