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	$187.91	5.617%	$198.4649	$198.46	$198.45	$198.50
Purchase #2	$28.60	12.309%	$32.1204	$32.12	$32.10	$32.10
Purchase #3	$40.36	3.555%	$41.7948	$41.79	$41.80	$41.80
Purchase #4	$118.85	3.575%	$123.0989	$123.10	$123.10	$123.10
Purchase #5	$145.31	12.858%	$163.994	$163.99	$164.00	$164.00
Purchase #6	$143.73	5.163%	$151.1508	$151.15	$151.15	$151.20
Purchase #7	$80.57	10.737%	$89.2208	$89.22	$89.20	$89.20
7 purchase totals =	$745.33		$799.8446	$799.83	$799.80	$799.90