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	$11.64	4.539%	$12.1683	$12.17	$12.15	$12.20
Purchase #2	$103.48	9.759%	$113.5786	$113.58	$113.60	$113.60
Purchase #3	$247.35	3.418%	$255.8044	$255.80	$255.80	$255.80
Purchase #4	$145.80	9.280%	$159.3302	$159.33	$159.35	$159.30
Purchase #5	$240.86	8.148%	$260.4853	$260.49	$260.50	$260.50
Purchase #6	$174.39	4.125%	$181.5836	$181.58	$181.60	$181.60
Purchase #7	$17.29	12.517%	$19.4542	$19.45	$19.45	$19.50
7 purchase totals =	$940.81		$1,002.4046	$1,002.40	$1,002.45	$1,002.50