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	$74.51	13.317%	$84.4325	$84.43	$84.45	$84.40
Purchase #2	$203.30	7.292%	$218.1246	$218.12	$218.10	$218.10
Purchase #3	$153.29	4.388%	$160.0164	$160.02	$160.00	$160.00
Purchase #4	$191.87	12.509%	$215.871	$215.87	$215.85	$215.90
Purchase #5	$181.83	4.276%	$189.6051	$189.61	$189.60	$189.60
Purchase #6	$85.85	11.260%	$95.5167	$95.52	$95.50	$95.50
Purchase #7	$93.31	5.409%	$98.3571	$98.36	$98.35	$98.40
7 purchase totals =	$983.96		$1,061.9234	$1,061.93	$1,061.85	$1,061.90