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	$33.91	10.582%	$37.4984	$37.50	$37.50	$37.50
Purchase #2	$221.68	7.712%	$238.776	$238.78	$238.80	$238.80
Purchase #3	$153.43	13.207%	$173.6935	$173.69	$173.70	$173.70
Purchase #4	$180.68	13.148%	$204.4358	$204.44	$204.45	$204.40
Purchase #5	$169.29	9.278%	$184.9967	$185.00	$185.00	$185.00
Purchase #6	$153.91	3.397%	$159.1383	$159.14	$159.15	$159.10
Purchase #7	$43.57	6.700%	$46.4892	$46.49	$46.50	$46.50
7 purchase totals =	$956.47		$1,045.0279	$1,045.04	$1,045.10	$1,045.00