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	$99.43	12.158%	$111.5187	$111.52	$111.50	$111.50
Purchase #2	$16.45	13.707%	$18.7048	$18.70	$18.70	$18.70
Purchase #3	$29.82	4.486%	$31.1577	$31.16	$31.15	$31.20
Purchase #4	$75.61	8.513%	$82.0467	$82.05	$82.05	$82.00
Purchase #5	$95.26	13.611%	$108.2258	$108.23	$108.25	$108.20
Purchase #6	$180.63	5.111%	$189.862	$189.86	$189.85	$189.90
Purchase #7	$192.94	10.417%	$213.0386	$213.04	$213.05	$213.00
7 purchase totals =	$690.14		$754.5543	$754.56	$754.55	$754.50