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	$36.37	13.365%	$41.2309	$41.23	$41.25	$41.20
Purchase #2	$211.96	13.286%	$240.121	$240.12	$240.10	$240.10
Purchase #3	$72.45	3.391%	$74.9068	$74.91	$74.90	$74.90
Purchase #4	$203.56	12.786%	$229.5872	$229.59	$229.60	$229.60
Purchase #5	$11.63	10.575%	$12.8599	$12.86	$12.85	$12.90
Purchase #6	$46.25	8.575%	$50.2159	$50.22	$50.20	$50.20
Purchase #7	$52.42	13.404%	$59.4464	$59.45	$59.45	$59.40
7 purchase totals =	$634.64		$708.3681	$708.38	$708.35	$708.30