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	$103.26	12.666%	$116.3389	$116.34	$116.35	$116.30
Purchase #2	$107.82	9.409%	$117.9648	$117.96	$117.95	$118.00
Purchase #3	$72.85	8.529%	$79.0634	$79.06	$79.05	$79.10
Purchase #4	$131.85	8.689%	$143.3064	$143.31	$143.30	$143.30
Purchase #5	$144.77	10.105%	$159.399	$159.40	$159.40	$159.40
Purchase #6	$78.98	12.769%	$89.065	$89.07	$89.05	$89.10
Purchase #7	$55.80	3.191%	$57.5806	$57.58	$57.60	$57.60
7 purchase totals =	$695.33		$762.7181	$762.72	$762.70	$762.80